- Author: Richard Smith
Weed control in lettuce and other crops is a key issue this time of year. Purslane is particularly problematic and is adapted to warm conditions and can grow very rapidly especially during July and August. At times growers and PCA's are disappointed with the efficacy of Kerb on this weed. Kerb is effective in controlling purslane but it is readily leached and, if applied at planting, it can be moved below the zone of germinating weed seeds with the germination water. For instance, 6-8 hours of sprinkler water (1.5 to 2.0 inches) are commonly applied in the first germination water which can move the Kerb below the upper 0.5 inch of soil which is the zone where the weed seeds germinate; the movement of Kerb with the germination water is particularly problematic on sandy soils. Prefar does not leach and thus provides most of the purslane control when the two materials are tank mixed (Figure 1). However, Prefar does not control shepherd's purse or nightshades which can also be problematic in lettuce fields. Therefore, it would be advantageous to optimize the efficacy of Kerb to maximize the control of purslane as well as other weeds.
In the desert, the use of delayed applications of Kerb has been used for many years. Due to the large amounts of water that are applied in their hot conditions, Kerb is applied in the 2nd or 3rd germination water, approximately 3-5 days following the first germination water, just prior to the emergence of the lettuce seedlings. This technique can also be utilized in the Salinas Valley. We have looked at this technique over the years and have found it to improve the efficacy of Kerb (Figure 2). These data illustrate the loss of control of purslane by Kerb when applied before the 1st germination water, as well as the improvement in efficacy that results when applied following the 1st germination water. It also illustrates the role that Prefar plays in the control of purslane when the efficacy of Kerb is lost by leaching. It should be mentioned that the label states that the maximum amount of Kerb that can be applied through the sprinklers is 2.5 pints/A and the amount used in this trial was for experimental purposes only. Clearly there is benefit from applying the Kerb later in the 2nd or 3rd germination water, however, we observed that applying the Kerb at the end of the 1st germination water also provided improved efficacy of Kerb. Clearly, anything that helps to keep the Kerb in the top 0.5 inch of soil improves its efficacy.
Here are some details that need to be considered regarding the application of Kerb later in the germination phase of the crop: There is a need to use an injection pump and tank. We have typically used a tank with a circulating mechanism to keep the Kerb in suspension while the injection was occurring. The material needs to be injected into the mainline in a location where proper mixing can occur before it begins to flow down the laterals. The most difficult issue that growers face is the compatibility of the injection with surrounding crops. This is probably the greatest challenge and must be carefully thought through before attempting an application.
Another idea that we explored last year was the use of an additive to help retain the Kerb in the upper portion of the soil where it can be most active. However, we did not see improved efficacy in two 2018 trials (data not shown).
Many growers now are now using drip irrigation to germinate lettuce. Grower may apply the same amount of water with drip germination as with sprinklers, but the movement of the water is different which affects a surface applied material differently. With this method of germination, there are a couple of interesting dynamics that occur: 1) Kerb is not pushed too deep by this germination method and effectively reduces weed populations whether injected into the germ water (currently not a registered method of application) or sprayed on the soil surface and activated by the drip germination water (Table 1); and 2) fewer weeds emerge with drip germination than with sprinklers, regardless of the herbicide program.
Table 1. Effect of Kerb application (at 3 pints/A) method (surface applied, drip injected or untreated) and irrigation method (surface tape, buried tape or sprinkler) on weed densities, lettuce stand and visual injury.
- Author: Cheryl Reynolds
Summer is here, and we're halfway through 2019 already! Why not get jump on finishing up your continuing education units by taking online courses from the UC Statewide IPM Program (UC IPM). If you are a license or certificate holder from the California Department of Pesticide Regulation (DPR), and your last name begins with the letters M through Z, you should be receiving your renewal packet in August.
We're excited to announce some changes.
- In January, we switched all of our online courses to a new learning system located at https://campus.extension.org/. This new system has extensive technical support, is easier to navigate, and is more stable than the old one. Note that the extension platform offers courses from all across the country, including several providers from California. Look for the UC IPM logo to be sure you are taking one of our courses.
- We are pleased to announce that a brand-new online course on the Fuller rose beetle was added to our citrus integrated pest management IPM series. Dr. Beth Grafton-Cardwell, a citrus IPM specialist and research entomologist, and Dr. Joseph Morse, emeritus professor of entomology, developed the course. The course describes the life cycle, natural enemies, and management of Fuller rose beetle and explains why it is important for countries that export citrus. Fuller Rose Beetle has been approved by (DPR) for 1 hour of credit in the Other category and by Certified Crop Advisor (CCA) for 0.5 hour of IPM credit.
- Many of our courses are now credited not only by DPR for continuing education hours, but also by the California Structural Pest Control Board (SPCB), Certified Crop Advisor (CCA), Western Chapter of the International Society of Arboriculture (WCISA), and also by Arizona Department of Agriculture.
DPR encourages license and certificate holders to avoid the end-of-the-year rush and submit renewal applications by November 1 to ensure license renewal by January 1, 2020. Submitting your renewal early avoids late fees and gives you time to address any issues that may arise such as not having enough hours to successfully renew.
Another incentive to get a jump on completing your needed continuing education units (CEUs) with UC IPM's online courses is that we are offering an early-bird price for four of our most wanted courses until November 1st.
- Proper Pesticide Use to Avoid Illegal Residues (2 hours Laws and Regulations; early bird price $40, full price $80)
- Proper Selection, Use, and Removal of Personal Protective Equipment (1.5 hours Laws and Regulations; early bird price $30, full price $60)
- Pesticide Resistance (2 hours Other; early bird price $20, full price $40)
- Pesticide Application Equipment and Calibration (1.5 hours Other; early bird price $15, full price $30)