Kassim Al-Khatib's Lab

About the lab

The most critical weed issue is the risk of weed and weed management strategies to the economy, human health, and the environment. Weeds reduce farm and forest productivity, affecting people's health and impacting natural resources. We can reduce the risk of weeds and weed management strategies by developing biologically based weed management systems that incorporate weed monitoring and threshold-based decision-making, biological and cultural controls, and reduced-risk herbicides. Our program focuses on developing weed management strategies for rice and other agronomical crops to solve important economic and environmental problems. In addition, it focuses on safe herbicide application and reducing off-target herbicide movement.

Featured research (8)

Clomazone is a widely used herbicide in California water-seeded rice for control of bearded sprangletop and watergrass. Generally, clomazone is applied to a flooded rice field at day of rice seeding. However, interest exist among growers to delay the clomazone application. Weather variability may encourage growers to practice Leathers method. Leathers method is the practice of draining the field 1 to 2 days after air seeding to encourage better and more uniform seedling establishment, then reflooding back to a 10- to 15-cm flood 4 to 7 days later. Therefore, the objective of this study was to evaluate grass weed control and rice response at four rates of clomazone, applied at two timings: at day of seeding (DOS) in a continuous 10-cm flood, and after Leathers method. This study was conducted in 2019 and 2020 at the Rice Experiment Station in Biggs, California. In 2019, there were no difference across clomazone rate on control of bearded sprangletop independently of application timing used; however, in 2020 bearded sprangletop control with clomazone applied after Leathers method was 70 to 71% across clomazone rate by 60 days after treatment (DAT), compared to 92 to 97% in the DOS applications. Watergrass control was 100% in 2019 across clomazone rate and application timing. However, in 2020 watergrass control was greater at the DOS application with 54 to 71%. Clomazone applied at the 0.7 kg ha ⁻¹ Leathers method resulted in 84% bleaching by 14 DAT and was similar across all Leathers method clomazone applications and the 0.7 kg ha ⁻¹ DOS application. There was no rice grain yield difference among all clomazone treated plots with the exception of the 0.7 kg ha ⁻¹ Leathers method interaction with the DOS applications.
Water-seeding is a common cropping strategy in mechanized rice systems. Water-seeding of rice can suppress grass weeds, but it can encourage aquatic weeds and grass ecotypes that escape deep floodwater. In addition, water seeding prevents many cultural methods of weed control and limits available herbicides. Selection pressure from a limited palette of herbicides has resulted in widespread resistance in California rice. This study examined a novel combination of drill seeding and a stale seedbed (“stale-drill”) as a means to use a nonselective herbicide to manage weeds before rice emergence. In 2016 and 2017, rice cultivar ‘M-206’ was drilled at a rate of 120 kg ha ⁻¹ to 1.3-cm, 2.5-cm, and 5.1-cm depths. Planting rice deeper than 1.3 cm delayed emergence by 3 to 4 days. A postplant-burndown (PPB) treatment of glyphosate at 870 g ha ⁻¹ was applied just prior to rice emergence. Treatment delays had mixed effects on weed control. Glyphosate PPB was more effective at controlling Echinochloa spp. in 2017, reducing density by 30%, 48%, and 73% at 1.3-cm, 2.5-cm, and 5.1-cm seeding depths, respectively. The greatest overall weed control either year was found with glyphosate + pendimethalin followed by penoxsulam + cyhalofop at 1.3-cm planting depth. Rice stand and yield components were more strongly affected by planting depth in 2017 than in 2016, possibly owing to cool weather immediately after seeding. Yields in 2017 were reduced in deeper plantings by up to 72%. Therefore, if the stale-drill method is implemented with higher-vigor cultivars or higher seeding rates, we see potential in this method as a useful tool for reducing herbicide-resistant weeds in rice fields.
Rice grown in the Sacramento Valley of California is predominantly water seeded (WS), by direct-seeding rice into flooded basins. The effects of flooded rice monoculture and limited herbicides have led to difficult-to-control weed populations, and widespread local herbicide resistance. A novel “stale-drill” rice establishment method has been under investigation in California, to address these constraints. Two rice varieties with high seedling vigor (‘M-206’, ‘M-209’) were dry-drilled to 3 cm and 6 cm in 2018 and 2019, and fields were flush-irrigated to initiate weed germination prior to stand emergence. A postplant-burndown (PPB) application of glyphosate at 870 g a.e. ha⁻¹ was applied 6-7 days after planting (DAP), at rice emergence, which controlled >50% of total seasonal weeds. Glyphosate PPB caused rice first-leaf dieback, but no other symptoms developed. Planting depth or cultivar did not affect date of emergence either year. Deeper seeding reduced M-206 and M-209 stands by 15.4% and 5.2%, respectively, in 2018, but not in 2019. Increased tillering compensated for stand reductions in 2018. Panicle yield components were largely unaffected by planting depth in 2018, however florets panicle⁻¹ and filled grains panicle⁻¹ were slightly greater for both cultivars at 6 cm. In 2019, M-209 suffered reductions in florets per panicle and grain filling at 6 cm planting depth. Grain yields were unaffected by planting depth in either study year. M-206 and M-209 grain yields were 10.2 T ha⁻¹ and 12.2 T ha⁻¹ respectively, in 2018, and 9.4 T ha⁻¹ and 9.1 T ha⁻¹ respectively, in 2019. Proper water management and scouting are essential to ensure that PPB treatments do not injure emerging rice to the extent that weak or reduced stands result. However, the present study serves as a promising proof-of-concept for the “stale-drill” method as an alternative stand establishment method in mechanized rice production.
Weedy rice ( Oryza sativa f. spontanea Roshev.) has recently become a significant botanical pest in California rice ( Oryza sativa L.) production systems. The conspecificity of this pest with cultivated rice, Oryza sativa (L.), negates the use of selective herbicides, rendering the development of non-chemical methods a necessary component of creating management strategies for this weed. Experiments were conducted to determine the emergence and early growth responses of O. sativa spontanea to flooding soil and burial conditions. Treatment combinations of four flooding depths (0, 5, 10, and 15 cm) and four burial depths (1.3, 2.5, 5, and 10 cm) were applied to test the emergence of five O. sativa spontanea accessions as well as ‘M-206’, a commonly used rice cultivar in California, for comparison. Results revealed that burial depth had a significant effect on seedling emergence. There was a 43-91% decrease in emergence between seedlings buried at 1.3 and 2.5 cm depending on the flooding depth and accession, and an absence of emergence from seedlings buried at or below 5 cm. Flooding depth did not affect emergence, but there was a significant interaction between burial and flooding treatments. There was no significant difference between total O. sativa spontanea emergence from the soil and water surfaces regardless of burial or flooding depths, implying that once the various accessions have emerged from the soil they will also emerge from the floodwater. Most accessions had similar total emergence compared to M-206 cultivated rice, but produced more dry weight than M-206 when planted at 1.3 cm in the soil. The results of this experiment can be used to inform stakeholders of the flooding conditions necessary as well as soil burial depths that will promote or inhibit the emergence of California O. sativa spontanea accessions from the weed seedbank.
California rice ( Oryza sativa L.) production has been recently challenged by the early season bloom of nuisance algae. The algal community in rice is a complex of green algae ( Nostoc spongiforme Agardh ex Bornet) and cyanobacteria species that could develop a thick algal mat on the surface of the water and interfere with the emergence and establishment of rice seedlings. The objective of this research was to determine the impact of algae infestation level on rice seedling emergence. A mesocosm study was conducted in 57 L tubs. Three levels of algae infestation (low, medium, and high) were produced by adding fertilizer N:P amount into the tubs including 0:0, 75:35, and 150:70 kg ⁻¹ ha. Sixty rice seeds (M-206) were soaked for 24 hours and spread into tubs filled with water. Photosynthetic Active Radiation (PAR), Chlorophyll a concentration as the quantitative measure of algae, number of emerged rice seedlings, and their dry biomass were studied during the experiment. Results showed that algae infestation can directly change the amount of light received into the water. Minimum, maximum and mean percentage of PAR inside the water declined by the increase of algae infestation level. As a consequence, rice seedling emergence dropped under the high algae pressure. At very high algae infestation (i.e. chlorophyll a concentration of above 500 µg ml ⁻¹ ), rice seedling emergence reduced up to 90%. Furthermore, rice seedling emergence was delayed under algae infestation. When algae infestation was low, time to 50% of rice seedling emergence (t 50 ) ranged between five and ten days, while at high algae infestation t 50 ranged between twelve and twenty days. Moreover, individual rice seedling biomass reduced from one gram to 0.01 gram by the increase of algae infestation. The results from this study indicate that uncontrolled algae at the beginning of the rice-growing season could reduce rice seedling emergence, establishment, and rice stand. Given that algae infestation in field has a patchy pattern, loss of rice stand in these patches could provide empty niches for other weeds to grow.

Lab head

Kassim Al-Khatib
  • Department of Plant Sciences

Members (3)

Deniz Inci
  • University of California, Davis
Liberty Galvin
  • University of California, Davis
Aaron Becerra-Alvarez
  • University of California, Davis

Alumni (5)

Junjun Ou
  • Corteva Agrisciences
Sara Ohadi
  • University of California, Davis
Whitney Brim-DeForest
  • University of California Division of Agriculture and Natural Resources (ANR)
Alex R. Ceseski
  • University of California, Davis