- Author: Lynn M. Sosnoskie
Agronomy and Weed Science Advisor, Merced County
It's getting hot and dry in the Central Valley and the movement of equipment in and out of fields/orchards/vineyards has the potential to stir up a significant amount of dust. Among its other impacts to agriculture (soil erosion, tissue damage, reduced photosynthesis, etc...), wind blown dust can reduce the efficacy of glyphosate, which is an important tool for the management of weeds in trees and vines, along rights-of-ways, and in glyphosate-tolerant agronomic crops (e.g. corn, cotton, alfalfa) in CA.
The adoption of glyphosate has been facilitated, at least in part, by it's relative lack of soil activity (Miller et al. 2013; Zhou et al. 2006). Glyphosate can become tightly adsorbed to soil particles (depending on clay and organic matter content, pH, cation exchange capacity, etc...), thereby reducing the potential for crop injury via root uptake. The ability of glyphosate to bind to soil also contributes to it's reduced efficacy in certain situations. Specifically, dust that settles on weed leaf surfaces (Figure 1) can negatively impact glyphosate performance due to binding/inactivation.
Figure 1. Dirt on field bindweed (Convolvulus arvensis) leaves
The detrimental effects of dust on glyphosate performance have been described by Zhou et al. (2006) and Boerboom et al. 2006). Results from Zhou et al. (2006) showed that dust applied to the surface of eastern black (Solanum ptychanthum) and hairy (Solanum sarrachoides) nightshades reduced weed control, with greater amounts of dust resulting in greater reductions in herbicide efficacy (Figure 2). In a study conducted by Boerboom et al. (2006), dust was deposited over the tops of plots of common lambsquarters (Chenopodium album); water was then used to remove the dust treatment from ½ of the plots prior to a glyphosate application. Similar to the results achieved by Zhou et al. (2006), the occurrence of dust visually reduced common lambsquarters control (relative to the plots where the dust had been washed away). Results from both sets of studies show that dust generation has the potential to significantly impact glyphosate performance'
Figure 2. Percent reduction in weed control by glyphosate as affected by the rate of a silty clay dust applied to the leaves of two nightshade species. Greater numbers on the Y-axis indicated greater reductions in control.
Adapted from Zhou et al. (2006) Weed Science 54:1132-1136.
A few closing thoughts about dust and it's impact on weed control:
- Be mindful of how soil disturbance (cultivation, farm traffic, etc...) affects dust production.
- Make glyphosate applications in advance of crop production events that are likely to generate substantial amounts of dust.
- Sprinkler irrigation may be able to remove dust from the leaves of weeds under some situations. Glyphosate applications should be made after the leaves have dried but before more dust can be deposited.
- Soil particles in spray water can also bind to glyphosate and reduce herbicide efficacy; only clean water should be used to fill spray tanks. (Not actually dust related, but a good practice to remember)
Citations:
Boerboom, C. et al. (2006) Factors affecting glyphosate control of common lambsquarters. Proceedings of the North Central Weed Science Society 61:54.
Miller, T. et al. (2013) Glyphosate stewardship: Maintaining the effectiveness of a widely used herbicide. ANR Publication 8492. https://anrcatalog.ucanr.edu/pdf/8492.pdf
Zhou, J. et al. (2006) Soil dust reduces glyphosate efficacy. Weed Science 54:1132-1136.
Note: An earlier version of this post is available at the following website: http://treefruit.wsu.edu/dust-can-affect-weed-control-with-glyphosate/
/h4>/h4>- Author: Shimat Villanassery Joseph
- Author: Mark Bolda
Lygus bug (Lygus hesperus) (Fig. 1) is a major pest of strawberry in the Central Coast. Lygus bug populations develop on weed hosts surrounding the strawberry fields such as wild radish, common groundsel, lupines, and mustards (Zalom et al. 2012). Time to time, adults migrate into the strawberry fields and lay eggs. Eggs hatch, and molt through five nymphal stages before molting into adults. Lygus bug feeding on the developing embryos affects the normal development of tissues surrounding the embryo (Handley and Pollard 1993) and affected fruits are misshapen often referred as “catfaced fruit” (Fig. 2) which are deemed unmarketable. Although both nymphs and adults can cause catface injury, nymphs are considered more destructive than adults. The young fruits up to ~10 days after petal fall are considered vulnerable to economic injury from lygus bug feeding (Zalom et al. 2012).
Chemical control continues to be an effective tool for lygus bug control and growers are always seeking effective and softer insecticides for its control. A replicated trial comparing the efficacy of insecticide treatments against lygus bug was conducted in first-year strawberry ‘San Andreas' in Watsonville, CA in 2016. The details on insecticide products and rates used in the trial are shown in Table 1. The insecticides were applied twice at 10 day interval using commercial tractor mounted sprayer. The water volume used for both the applications was 150 gal per acre and was applied at 140 psi. Dyne-Amic (surfactant) was added at 0.25% v/v to all the treatments. Insect samples were collected using regular sized Rubbermaid container by hitting 20 flowering strawberry plants with lid. In addition, 60 fruits were sampled from each plot to determine catface injury.
Pre-count sample did not show any difference in number of adult and nymphal lygus bugs among treatments (Figs. 3 and 4). Overall, all the insecticide treatments reduced the number of lygus bug adults and nymphs compared with untreated plants. The combination treatments using pyrethroid insecticides such as Danitol and Brigade suppressed lygus bugs and general predators such as bigeyed bug, minute pirate bug, and damsel bug as well as spiders (Figs. 5-8). Data show that reduced-risk insecticides, Rimon and Beleaf suppressed lygus bug nymphs as well. Sequoia, not yet registered on strawberry, provided a decent lygus bug control. Sivanto initially provided a good suppression of adults and nymphs but could not adequately sustain the control for more than a week. Two rates of Avaunt (unregistered insecticide on strawberry) was included in this experiment and were comparable to other effective insecticides in this experiment.
Insecticide use certainly reduced catface injury on strawberry fruit. Number of fruits with catface injury was lower in all the insecticide treated plants than untreated except the lower rate of Avaunt (Fig. 9). Catface injury on fruits treated with Sequoia was lower than untreated but not different from other insecticides (except lower rate of Avaunt).
References
Handley, D. T., and J. E. Pollard. 1993. Microscopic examination of tarnished plant bug (Heteroptera: Miridae) feeding damage to strawberry. J. Econ. Entomol. 86: 505-510.
Zalom, F. G., M. P. Bolda, S. K. Dara, and S. Joseph. 2012. Strawberry: Lygus bug. UC Pest Management Guidelines, UC ANR Publication 3468. http://www.ipm.ucdavis.edu/PMG/r734300111.html