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COMPLEMENTARY INTERACTIONS BETWEEN WEEDS, WEED CONTROL PRACTICES,
AND PESTS IN HORTICULTURAL CROPPING SYSTEMS1
R. D. William
Departm ent o f Horticulture, Oregon State University, Corvallis, OR 97331
Throughout the world, growers of horticultural crops employ a mul
titude of crop and pest management practices designed to reduce pests
and minimize crop losses. Although weeds continue to afflict humans
(65), host other pests (14), and cause appalling crop losses on a world
wide scale (66, 109, 110), certain weedy2 species may complement hor
ticultural cropping systems. This paper reviews entomological, patho
logical, and crop-related literature where manipulation of a specific
weed, a weed control practice, or a cropping system can suppress a
crop pest. Perhaps horticulturists and colleagues will recognize an op
portunity to improve our understanding and our ability to successfully
manage one or more of the following examples, thereby improving
production efficiencies within modern horticultural cropping systems.
Weeds and weed control practices that interfere with pest establish
ment
Many insect and parasite pests respond to stimuli that cause the pest
to accept or reject a host plant or habitat. Examples include response
to visual, olfactory/chemical, or microenvironmental cues, or to physi
cal barriers such as windbreaks, intercrops, and surrounding vegetation
(8, 10, 13, 75, 79, 84, 90, 114, 140, 149). Various crop management
practices, or certain weedy species within or surrounding a crop field
can provide or alter these stimuli.
Visual interference. Specific colors or contrasting crop and soil back
grounds are used by some insects, such as the migrating alate aphid,
whitefly and other Homoptera, to locate host plants. For example,
various tints and hues of yellow attract at least 3 aphid species (79,
135). Similar crop and weed colors may provide specific cues needed
for this yellow-sensitive aphid to alight and begin probing on a host.
Some aphids and their natural enemies also respond to contrasting
crop and bare soil backgrounds. In crucifers, several aphids [Brevico-
ryne brassicae (Linnaeus), Aphis fabae Scopoli, and Myzus persicae
(Sulzer)]3 and a syrphid predator (Platycheirus sp.) preferred bare soil
backgrounds (3, 37, 105, 116, 137, 138, 139), whereas another enemy
(Melanostoma sp.) preferred a weedy background (139). Increased
aphid density and virus transmission was associated with contrasting
crop and soil backgrounds in peanut (Arachis hypogaea L.) (1, 2, 17,
70), sugar beet (Beta vulgaris L.) (61), and horse bean (Vicia faba L.)
(152). Similarly, whitefly [Aleyrodes brassicae (Wlk.)] (138) incidence
and oviposition of corn borer (Ostrinia sp.) (71, 72) were increased
when crops were grown on bare soil backgrounds compared to weedy
or intercropped peanut and artificial green backgrounds.
In addition to improved yields and crop quality, opaque mulches
often reduce weed growth and interfere with pest incidence. Following
a report that aluminum foil altered the direction of aphid flight (78),
many examples have been published about reflective mulches and
treatments that reduce insect attraction and delay spread of transmitted
viruses (Table 1). Aluminum mulches, for example, discourage aphids
and other insects from alighting on crop plants, whereas white and
black polyethylene mulches cause moderate rejection. Honey bees
were attracted to aluminum mulch, but were discouraged by hanging
aluminum reflectors (154). Whitefly were attracted preferentially to
yellow plastic or straw mulching materials rather than a crop, thereby
delaying virus infections. (18, 26, 104).
Tillage practices also modify crop appearance and can reduce pest in
cidence. Minimum-till corn (Zea mays L.) had fewer lesser cornstalk
borers [Elasmopalpus lignosellus (Zeller)] because these facultative
saprophytes fed on surface debris, whereas the pest fed on corn plants
in conventional tillage (5). In Asia, farmers often broadcast southern
peas [Vigna unguiculata (L). Walp.], and mungbean [V. radiata (L.)
Wilzcek], or dibble soybean (Glycine max L.) near rice stubble. Recent
studies in the Philippines demonstrated that 15 cm rice stubble reduced
beanfly [Ophiomyia phaseoli (Tryon)], thrip ( ThripspalmiKarny), and
leafhopper [Empoasca biguttula (Shiraki)] incidence in southern peas
(130).
’Oregon State University Agricultural Experiment Station Technical Paper No.
5683.
2 Weeds, weedy plants, or wild plants will refer to plants or cover crops that nor
mally lack direct economic value within a horticultural cropping system.
3Common and scientific names of insects cited from Sutherland, D.W.S. (ed.)
1978. Common names of insects and related organisms. Entomological Soc. of
Amer., College Park MD 20740.
Olfactory or chemical interference. Weeds or rotational plants may
produce odors or organic compounds that modify pest behavior. Cru
cifers, for example, produce isothiocynate which volatilizes from soil
during growth and attracts the diamondback moth [Plutella xylostella
(Linnaeus)] (149), but inhibits emergence of cyst nematodes (Hetero-
dera sp.) from infected roots (41, 42, 150) and prevents pea root rot
(Aphanomyces euteiches Drechsler) (85). Exudates from bean (Pha-
seolus vulgaris L.) roots stimulate germination of Fusarium that incites
root rot [F. solani (Mart.) Appel & Wr. f. phaseoli (Burk.) Snyd. &
Hans.] (131), but rotations with barley (Hordeum sp.) inhibit infection
because decomposition of the straw reduces nitrogen availability (157).
Continuous potato (Solanum tuberosum L.) (156) or potato and soy
bean rotations (129, 156) enhance bacterial populations of Bacillus
subtilis Coin, which antagonize potato scab [Streptomyces scabies
(Thaxter) Waksman and Henrici] (155). Certain genetic strains of oat
(Avena sp.) (48) and cucumber (Cucumis sativus L.) (91, 121), or
residues of cover crops (120) produce allelopathic exudates that inhibit
weed seed germination.
Interplanting crops such as crucifers with tomato (Lycopersicon es-
culentum Mill.) (21, 72, 115, 146), or ragweed (Amborsia artimisiifolia
L.) (146) interfered with olfactory responses and reduced incidence of
diamondback moth (115, 146), whitefly (115), and flea beetle (Phyllo-
treta cruciferae Goeze) (146), whereas several oth er interplants did not
interfere with crucifer pests (80). Beans interplanted or surrounded
with goosegrass [Eleusine indica (L.) Goertn] and sprangletop [Lep-
tochloa filiformis (Lam.) Beauv.] interfered with colonization and re
production of leafhopper (Empoasca kraem eri Ross & Moore) (8).
French marigold (Tagetes patula L.) interplanted between beans inter
fered with Mexican bean beetle (Epilachna varivestis Mulsant) infesta
tions, but allelopathic or competitive effects also reduced bean growth
(81).
Repeated spray applications of extracts of goosegrass and sprangle
top (8) or thyme ( Thymus vulgaris L.) and sage (Salvia officinallis L.)
(93) interfered with infestations of leafhopper in beans and imported
cabbage worm [Pieris rapae (Linnaeus)] in crucifers. In contrast, para
site density within soybean fields increased with single applications of
pigweed (Amaranthus sp.) extracts (12).
Preferred hosts and decoy interference. Both crop and wild plants
often function as preferred hosts for pests. Black cutworm [Agrotis ip-
silon (Hufnagel)] and other lepidoptera larvae feed preferentially on
spiny amaranth (Amaranthus spinosus L.) rather than beans (53), cu
cumbers (personal observation), or tomatoes (W.M. Stall, University
of Florida, personal communication). In corn, a leafhopper [Graminel-
la nigrifrons (Forbes)] preferred weedy grass plots and transmitted less
corn stunt virus than in weed-free plots where leafhoppers fed only on
corn (117). Similarly, incidence of tobacco rattle virus (TRV) in pota
toes was reduced in plots containing preferred weed hosts for stubby-
root (Trichodorus sp.) nematodes compared to weed-free plots (29). In
California, lygus bugs (Lygus sp.) preferred strips of alfalfa (Medicago
sativa L.) which represented only 6% of the field rather than cotton
(Gossypium sp.) (144).
Some plants function as decoys by attracting insects or pathogens.
Mortality or reduced fecundity may result if these plants contain toxins
or lack a balanced diet for insect development. Black nightshade (Sola
num nigrum L.) functions as a decoy plant in potatoes where the Colo
rado potato beetle [Leptinotarsa decemlineata (Say)] oviposites prefer
entially, but the larvae die because neither the adult nor larvae feed on
the weed (67). Although few examples of interference with plant path
ogens exist, decoy plants may stimulate germination of certain soil-
borne pathogens resulting in their death because suitable host plants
are unavailable (157).
Physical interference in habitat. Selection of field sites, crops, rota
tions, and other management practices influence survival of pests and
their associates. Windbreaks, hedgerows, or other barriers to air flow
create sheltered areas on the leeward side where alate aphids (44, 60,
86, 87, 88) and pollinating insects (89) collected in row crops and or
chards, although one study reports no differences (118). Interplanting
corn in sweet potatoes [Ipomoea batatas (L.) Lam.] appeared to inter
fere with 2 beetle pests (Diabrotica sp.) when the corn was taller than
50 cm (127). In one study, however, infestations of brown soft scale
(Coccus hesperidum Linnaeus) increased with greater distance from
Species involved (literature citation)
Mulch or
reflective treatment Flowers Edible legumes Cucurbits Lettuce Tomato
Alum inu m foil
Mulches Aphid & CVM (73) Leafminer (154) Aphid (159) Aphid & CMV (102) Aphid (159)
Thrip (107, 134) Leafhopper (23, 24) Aphid & WMV (4, 25, 38, 54, 161)
Mexican bean beetle (136) Honey bee (159)
Reflectors Aphid & CMV (73) Aphid & WMV (32) Aphid (159)
Green peach aphid (159)
Honey bee (159)
Leafminer (159)
Paint or spray
Polyethylene mulch
Aphid (73) Leafminer (154)
Aluminum Aphid & CMV (73) Aphid (149) Aphid (159)
Aphid & WMV (16)
Leafminer (16)
Honey bee (159)
Whitefly & TYLCV (27)
White Aphid & CMV (73) Leafminer (154) Aphid (16, 149)
Aphid & WMV (16, 161)
Honey bee (159)
Leafminer (16)
Black Aphid & CMV (73) Leafminer (154) Aphid (159) Aphid (159)
Aphid & WMV (4,54) Leafminer (119)
Whitefly & TYLCV (27)
Fiber mulches
Paper Leafhop per (23, 24) Aphid & WMV (16)
Pickleworm (16)
Leafminer (16)
Straw Leafhopper (130)
Thrip (130)
Whitefly & BGMV (104) Whitefly & TYLCV (27)
zNames and groupings of plants include gladiolus (Gladiolus hybr. L) and rose (Rosa sp.); dry bean (Phaseolus vulgaris L.) and southern pea [Vigna unguiculata (L.)
Walp]; cucumber (Cucumis sativus L.), summer squash (Curcurbita pep o L., melopepo group), cantaloupe (Cucumis melo L.), and watermelon [Citrullis lanatus
(Thumb.) Matsum & Nakai]. Insects included aphid mixtures or green peach aphid [Myzus persicae (Sulzer)]; gladiolus thrip [Taeniothrips simplex (Morison)], leafbud
feeding thrip ( Thripspalmi Karny); leafminer (Liriomyzas sp.); leafhopper [Empoasca biguttula (Shiraki) & E. kraemeri Ross & Moore); Mexican bean beetle (Epilach-
na varivestis Mulsant); tobacco whitefly [Bemisia tabaci (Gennadius)]; pickleworm [Diaphania nitidalis (Stoll)]; and honey bee (Apis mellifera Linnaeus). Viruses in
cluded cucumber mosaic virus (CMV), watermelon mosaic virus (WMV), bottle gourd mosaic virus (BGMV) and tomato yellow leaf curl virus (TYLCV).
the hedgerows in citrus (125).
Modifications of the crop or intercrop leaf surface can influence pest
infestations. Dust from roads or clean cultivation can modify habitats
on leaf surfaces resulting in less parasitization or California red scale
[Aonidiella aurantii (Masked)] in citrus (36), and predation of Wil
lamette mite (Eototranychus willamettei Ewing) in vineyards (50), or
red spider mite (Oligonychus coffeae Neit.) in tea [Camellia sinensis
(L.) Kuntze] (33). In Malawd, bean epidermal hairs trapped aphids and
reduced transmission of rosette virus disease in peanuts when inter-
planted in alternate rows (47).
Weeds host beneficial species
Herbaceous weeds often provide food, shelter, or alternate hosts for
neutral and beneficial species within or surrounding agricultural fields.
These beneficial weed and insect species contribute to pest control by
providing requisites for predators and plant parasites.
Wild flowers provide pollen and nectar.4 Many parasitic Hymenopte-
ra require carbohydrates, specific amino acids, or other dietary com
pounds obtained from pollen or nectar of weedy plants or from body
fluids of host insects. Wild flowers and flowering weeds, lor example,
attracted parasites within wheat (Triticum sp.) or cabbage (Brassica
oleracea L., capitata group) fields (43). In an apple (Malus sp. Mill.)
orchard, wild flowers attracted parasites and increased parasitization of
codling moth [Laspeyresia pomonella (Linnaeus)] and tent caterpillar
[Malacosoma americanum (Fabaricius)] by 4 to 18 times (82). Al
though many flowering plants attract beneficial insects, Umbelliferae
flowers seem especially attractive to several parasitic wasps and can
provide essential compounds for survival and fecundity (77, 82, 158).
Presence of wild carrot (Daucus carota L.) was required for successful
introduction of a par as it e of Jap ane se beetle (Popillia japonica New
man) (77). In Puerto Rico, a parasite of mole cricket (Scapteriscus vic-
inus Scudder) required nectar from 2 weeds [Borreria verticillata (L.)
G.F.W . Mey and Hyptis atrorubens Poit.) for successful establishment
(158).
Weedy sites that contain ample pollen as alternate food sources often
harbor more stable populations of predaceous mites, syrphid larvae,
and coccinellids (44, 68, 123). In vineyards, for example, incidence of
Willamette mite was suppressed when populations of a predator mite
[Metaseiulus occidentalis (Nesbitt)] were maintained throughout the
season by preying on other mites which fed on Johnsongrass [Sorghum
^Examples from Soviet literature are cited by 10, 44, 45, 60, 92 and 101.
halepense (L.) Pers.] pollen (49) or cattail (Typha sp.) pollen applied
artificially (60). Syrphid flies required pollen for egg production (18,
60) and preferred weedy oviposition sites along crucifer and pea (Pi-
sum sativum L.) fields (45, 51).
Weeds host herbivores and supplement arthropod food chains. Wild
plants and crops form the base of the food chain for insects. Goldenrod
(Solidago altissima L.) (9), stinging nettle (Urtica dioica L.) (113),
Spanish needle (Bidens pilosa L.) (103), pepperweed (Lepidium alys-
soides L.) (128), ragweed (56, 142) and many other wild plants are re
ported to host large populations of herbivores which, in turn, provide
reservoirs of prey for beneficial predators and parasites.
Management or destruction of herbaceous plant communities grow
ing within or near agricultural fields can regulate certain crop pests by
increasing stability of herbivore and natural enemy populations. Main
tenance of aphid populations on weeds or vetch ( Vicia sp.) increased
predatory coccinellids (ladybeetles) within walnut (Juglans regia L.)
(133) and pecan (Carya illinoinensis L.) W.L. Dders, University of
Georgia, personal communication) orchards, whereas stinging nettle
maintained aphid populations surrounding cultivated fields (113). In
terplanting corn with soybean (20), bush beans (22), or several low-
growing weeds (11) increased egg predation of fall army worm [Spo-
doptera frugiperda (J.E. Smith)], whereas interplanted weeds did not
influence predation of corn earworm (11). In contrast, timely destruc
tion of vetch interplanted in pecan orchards (W.L. Dders, pers.
comm.) or weeds such as stinging nettle (113) can force movement of
natural enemies into the crop resulting in suppression of crop pests.
Weeds bridge life-cycle gaps. Certain natural parasites of crop pests
require alternate hosts to bridge life-cycle gaps. Parasitized larvae in
festing ragweed and smartweed (Polygonum sp.) or the larvae of the
strawberry leafroller (Ancylis comptana fragariae (Walsh and Riley)]
appeared to be associated with increased parasitization of the oriental
fruit moth [Grapholitha molesta (Busck)] in weedy peach [Prunus per-
sica (L.) Batsch] orchards (112) and nearby strawberry (Fragaria X
ananassa Duch.) fields (6). In California, a leafhopper parasite (Ana-
grus epos Girault) breeds throughout the year in leafhopper nymphs
[Dikrella cruentata (Gillette)] found in wild Rubus. The parasite re
sponds seasonally to the grape leafhopper (Erythroneura elegantula
Osborn) found in some California vineyards when wild grape ( Vitis ca
lif ornica Bentham.) grows nearby (39). Another effective parasite
[Horogenes fenestralis (Holmgren)] of diamondback moth emerges
from cocoons in the fall and overwinters in an alternate host (Swam-
merdamia lutaria (Haworth)] or hawthorn (Crataegus sp.) (cited by
45).
Weeds provide shelter. Several insects seem to respond only to in
creased shelter. Activities of ground-dwelling beetles (carabids) and
spiders (phalangids) increased when sheltered with white or red clover
(Trifolium repens L. and T. pratense L.) intersown beneath crucifers
for control of imported cabbage worm (37, 105). Weeds or a legume
cover crop seemed to impede the flight and ground movement of rhi
noceros beetle [Oryctes rhinoceros (L.)] which reduced injury of young
oil palms (Elaeis gumeensis Jacq.) (160). Provision of an artificial band
around individual peach trees (148) or weeds and moss in an aban
doned orchard in England (28) improved shelter sites and increased
numerous predators and parasites in these orchards.
Managing complementary weed and crop interactions
The spatial and temporal boundaries of a crop are wider than com
monly perceived by most production managers and horticulturists.
With few exceptions, complementary crop and weed management
strategies involve year-round life-cycle interactions within and sur
rounding crop fields. Specificity and timeliness between interacting
species appear to be important criteria for successful management of
these strategies in horticultural cropping systems.
Field perimeters. Managing areas adjacent to agricultural fields can
reduce habitats for many crop pests and improve control of both pest
and beneficial species within crop fields. Hedgerows and windbreaks,
for example, increased leeward deposition of small flying insects and
pollinators (44, 45, 63, 88). Rather than burning or destroying habitats,
maintenance of non-vector plants in adjacent grass or weedy strips,
brushy fence rows, windbreaks, or nearby forests can provide shelter
and oviposition sites (44, 51), increase food reservoirs (9, 10, 113, 158),
bridge life-cycle gaps (39), or interfere with the pest’s ability to locate
the crop (8).
Trap crops can preferentially attract pests from crops or provide
temporary resources'for beneficial organisms. Some pests remain pre
ferentially in the trap crop (74) or require control prior to harvest of ad
jacent crops or destruction of weedy perimeters. In contrast, timely de
struction of stinging nettle forced movement of predators into bean
fields (113). Also, strip harvesting of alfalfa successfully maintained
beneficial insects within large alfalfa fields in California (7).
Perennial cropping systems. Planting cover crops, maintaining per
manent sod, or managing weedy plant growth within many orchards
and plantation crops has replaced clean cultivation and thereby re
duced dust and decreased mite infestations. Sod or cover crops have re
duced nematode infestations in peach (97), Verticillium wilt in olive
(Olea europaea L.) (157), and numerous insect pests in peach (8, 112,
147), apple (28, 40), walnut (133), pecan (W.L. Dders, pers. comm.),
citrus (36), grape (50), tea (33), and oil palm (160). In walnut (133) and
pecan cropping systems (W.L.Dders), timely destruction or maturation
of the cover crop caused predacious coccinellids to seek aphid prey in
the trees.
Ann ua l cropping systems. Timely, year-round management of fallow
fields, tillage systems, and cultural practices can alter pest populations
during the cropping season and improve crop protection strategies for
production of annual crops. Planting cover crops that resist nematodes
(Table 2) and controlling susceptible weeds during both the cropping
and fallow seasons (15) can reduce nematode populations to the extent
that moderately tolerant crops can be grown with minimal crop injury
(126). Improved management of crop rotations (85, 155,156,157), and
decoy hosts (157) or improved knowledge concerning the ubiquitous
mycorrhizal root parasite Endogone (55, 96) can reduce infestations or
add protection from soil-borne pathogens. Year-round management of
sequential cropping systems (Table 3) can alter populations of nema
todes, soil-borne pathogens and weed species depending on choice of
crops within the sequence (145).
Seasonal soil disturbance and selection of various tillage systems can
suppress pests by altering plant and associated insect species within
agricultural fields. Plowing at various times throughout the year result
ed in varying population densities of weed species (9, 10, 76). Specific
herbivores and, in turn, predator populations, fluctuated according to
abundance of preferred weed and herbivore hosts (9, 11). In another
study, soil cultivation in winter destroyed many aphid parasites in brus-
sels sprout (Brassica oleracea L., gemmifera group) fields (153),
whereas shallow plowing with discs increased parasites of sugar beet
pests compared to moldboard plowing (Soviet research reviewed by 18,
143). Surface debris in no-till corn provided alternative food sources
and reduced infestations of lesser cornstalk borer (5), whereas planting
into rice stubble reduced several pests of legume crops (130).
Crop production practices can modify both the physical environment
within the crop field and the resulting population of associated orga
nisms. Mulching with straw or various colors of polyethylene (Table 1),
modifying plant densities and planting arrangements (3, 17, 61, 70, 95,
116, 152), managing weedy backgrounds (31, 105, 137, 138, 139), or
manipulating harvest methods and dates (7, 95, 144) will interfere with
colonization of some pests or improve the habitat for beneficial species.
Managing narrow strips of weeds (11) or preferably interplanting crops
(20, 21, 22, 47, 71, 95, 115, 127, 144, 146) might also enhance popula
tions of beneficial species.
Futuristic cropping systems may be enhanced with allelopathic sub
stances produced from cover crop residues (120) or crop cultivars (122)
that suppress germination of weed seeds. Complementary interplants
Table 2. Cover crop or weed species reported to host low, medium or high population densities of parasitic nematodes (literature citation).
Cover crops or weeds
Rootknot
(Meloidogyne sp.)
Lesion
(Pratylenchus sp.)
Sting
(Belonolaimus sp.) Other2
Composites
African marigold (Tagetes erecta L.) Low (34, 151) Low (94, 106, 132, 151)
French marigold (T. patula L.) Low (59, 151) Low (59,62 ,98, 132, 151) Stunty (98, 106)
Wild marigold (T. minuta L.) Low (34, 57y) Low (19) Low (19) Stubby-root & dagger (19)
Chrysanthemum x moriflorium Ram at. Low (59) Low (59)
Eriophyllum lanatum (Pursh.) J. Forbes Low (62)
Gaillardia x grandiflora Van Houtte Low (62)
Helenium x ‘Moerheium Beauty’ Low (62)
Horseweed [Conyza canadensis (L.) Crong.] Low (64)
Legumes
Hairy indigo (Indigofera hirsuta L.) Low (99y, 126) Low (19, 108, 126)
Caster bean (Ricinus communis L.) Low (59) Low (59)
Crotalaria sp.y Low (57,97, ll l y, 151) Low (151) Low (19, 57, 64) Burrowing (16),
Stubby-root & dagger (57)
Florida beggarweed [Desmodium tortuosum (SW) D.C.] Lowy (57), med. (99) High (108)
D. sandwicense E. Meyer [D. uncinatum] High (99)
D. intortum (Mill) Urb. Low (99)
Mucana deeringiana (Bort.) Merrill. [Stizolobium] Low (99)
Sesbania macrocarpa Muhlenb. High (126) High (108, 126)
Miscellaneous
Aesch ynom ene americana L., Alysicarpus vaginalis Lowy (99)
(L.) D .C., Cajanas cajan (L.) Huth., Dolichos Lowy (99)
lablab L., Glycine wightii (R. Grah. ex Wight Lowy (99)
and Arn.) Verdcourt, G. javanica L., Lupinus Lowy (99)
albus L., L. lutens L ., Phaseolus atropurpurens, Lowy (99)
& Stylosanthus humilis H.B. and K. Lowy (99)
Others
Mexicantea (Chenopodium ambrosioides L.) Low (64)
Shattercane [Sorghum bicolor (L.) Moench] Med. (126) High (126)
Scientific names include: Stunt (Tylenchorhynchus sp.), Stubby-root ( Trichodorus sp.), dagger ( Xiphinema sp.), and burrowing (Radapholus sp.) nematodes.
yPopulation densities vary, depending on nematode or host species.
Table 3. Year-round crop rotations that affect nemato de, soil-borne disease, and weed populations, Georgia,
1972 to 1974 (adapted from 145).
Crop rotation Nematodes suppressed2
Soil-borne pathogens
Fusarium Pythium Yellow nutsedgey
Turnip-corn-snapbean Stubby-root Moderate
Turnip-corn-turnip Stubby-root Low Low
Turnip-peanut-snapbean Spiral & stubby-root High Moderate
Turnip-peanut-turnip Lesion Moderate
T urnip-cuc. -so. pea-turnipx Ring & lesion Moderate High
Snapbean-soybean-cabbage Ring High Moderate
Scientific names include: stubby-root (Trichodorus sp.), spiral (Rotylenchus sp.), lesion (Pratylenchus sp.),
and ring (Criconemoides sp.).
ylnfestations of yellow nutsedge (Cyperus esculentus) increased in herbicide treated plots, whereas pigweed
(Amaranthus sp.) increased in cultivated plots.
xTurnip-cucumber-southern pea-turnip.
may produce exudates that promote metabolite exchanges and increase
absorption of nutrients (Soviet research cited by 122). Improved tillage
systems may encourage the planting of vegetables into living mulches
(69) or relay-interplanting vegetables before harvest of a previous crop
similar to conventional multiple cropping systems employed in the
tropics. Or perhaps crops will be sprayed with plant extracts or synthet
ic compounds that attract beneficial species (12), repel crop pests (9,
93, 115), or inhibit development of a pest (67).
Managing horticultural agroecosystems
Agroecosystems can be viewed as mixtures of cultivated and unculti
vated units where movement of organisms occurs between units and
where man subsidizes production with added energy and regulation
(92, 124). Crops are the central element in an agroecosystem (124) and
yield or profit stability continue to be primary goals of modern agricul
ture (84, 100).
Successful management of agroecosystems requires knowledge and
understanding or organism life-cycles and interactions at the communi
ty level within the surrounding crop fields (30, 35, 46, 58, 84, 100, 124,
140). Successful crop protection (pest management) involves strategies
designed first to prevent pests from reaching an action or economic
threshold, followed by regular monitoring of species within and sur
rounding crop fields (124). Temporary suppression of pest infestations
using pesticides occurs when an action threshold is reached for a specif
ic pest or pest complex (124).
Precision agriculture in the twenty-first century will require both
specialized disciplinary research and integrated studies designed to
identify manageable variables (35, 46) within and between trophic lev
els of an agroecosystem (84, 141), and to provide both optimal and op
tional crop protection strategies (124) for modification and adaptation
by growers. As complexity of modern and futuristic cropping systems
increase, our understanding of interactions and ability to manage pro
duction systems using modern computer technologies (52, 83, 124) sim
ilar to those used in industrial manufacturing and engineering systems
will undoubtedly occur (D. Tesar, University of Florida, personal com
munication). Twenty-first century growers will monitor numerous pro
duction factors including environmental conditions, crop growth rates,
soil and plant nutrients, moisture levels, pest populations, and inci
dence of beneficial species before accessing a computer via telephone
to compare these data with predictive crop models containing current
knowledge about the crop and possible interactions. Additional infor
mation such as least-cost fertilizers or pesticides; cost/benefit ratios for
various crop protection strategies; seasonal variability for growth, pest
populations, and marketability of products within local and national
regions; and many other data items could be compared to improve pro
duction decisions and marketing efficiencies. If nothing else, compu
ters will store vast amounts of information which can improve our un
derstanding of the complexities of modern agroecosystems and can
alert growers and horticulturists of possible interactions.
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