Early Season Weed Control FAQs

05-13PGcvrAs always, good management depends on proper application timing in relation to weed size.
By Ramon Leon and Jason Ferrell, University of Florida, Institute of Food and Agricultural Sciences

Editor’s Note: Two University of Florida weed researchers offer answers to some frequently asked questions regarding yellow herbicide applications, timing and crop injury. Use these answers to guide your weed management early on.

Q. Can I apply a yellow herbicide (Prowl, Sonalan) with Valor?

A. Yes, but you need irrigation to make this work at peak performance. The yellow herbicides are prone to degradation from sunlight if it lays on the soil surface for more than a few days. Both the Prowl H2O (pendimethalin) and Sonalan (ethalfluralin) labels suggest that incorporation should occur within 48 hours of application.

Tillage has traditionally been used to incorporate these herbicides into the soil with excellent results. However, the Valor (flumioxazin) label clearly states that mechanical incorporation will reduce the activity of this herbicide.

Considering these conflicting scenarios, there are two options: One option is to incorporate with irrigation or rainfall. Applying one-half to one inch of water will incorporate all of these herbicides, and no further activities would be required for optimum performance.

The second option is to apply them separately. If irrigation is not available and rainfall is not eminent, apply the yellow herbicide followed with mechanical incorporation. Then, apply Valor within three days after peanut planting. Rainfall is needed to activate the Valor, but it does not require immediate incorporation.

Q. Do I lose efficacy if Valor is applied prior to planting?

A. Yes, you might lose residual control during the growing season and allow weed emergence within the planting row.

Depending on how long before planting you spray Valor, you might be losing late-season residual weed control. Besides the good control Valor provides of important weed species, such as Palmer amaranth, that emerge early during the season, you will want to take advantage of the potential this herbicide has for controlling late-emerging species such as Florida beggarweed and morningglories.

Valor is a herbicide with very low mobility within the soil, so once you apply it, it is important to avoid soil disturbance. If Valor is applied before planting, and then the soil is disturbed for planting the seed, the herbicide layer on the ground will not be as uniform in this area where it is needed most. This is exactly the situation to avoid in the planting row so that weeds do not grow and compete right next to peanut plants.

Plant peanuts first and then spray the herbicide (PRE application). Make sure that Valor is applied no later than three days after planting and before cracking, otherwise peanut injury is likely. Remember, if the application is made at the right time, you will be taking full advantage of the benefits Valor can give you as a weed control tool.

Q. How much Basagran should I mix with paraquat for the “at cracking” spray?

A. Basagran may not be required at all.

Basagran has traditionally been used with paraquat to reduce peanut injury. However, numerous experiments have shown that this early season paraquat injury rarely translates into peanut yield loss. Furthermore, the addition of Basagran has not been shown to improve peanut yield and commonly adds minor weed control benefits.

If you do not wish to spray paraquat alone, adding Storm might be a better option. Storm, which contains the active ingredients of both Basagran and Ultra Blazer, can help reduce the paraquat burn while improving both morningglory and pigweed control over paraquat alone.

Q. Is applying Cobra with crop oilconcentrate too injurious?

A. No, Cobra (lactofen) plus crop oil concentrate will cause visible leaf injury (pictured above, left), but peanut plants will quickly recover (above, right) and no yield reductions should be observed.

Cobra can cause severe peanut injury when applied with crop oil concentrate. The most common symptoms of injury are mainly speckles of dead tissue on the leaf blade.

Our studies have shown that applying Cobra with crop oil concentrate at 15, 30 or 45 days after planting (DAP) can cause up to 30 percent injury seven days after treatment. However, despite this level of injury, which might make growers nervous, peanut plants will quickly produce new leaves, and usually a week later the injury is minimal. Very soon the plants are fully recovered, and by the end of the season, yields are not reduced.

An important detail is that the earlier you spray, the higher the injury, but this does not mean that you have to delay your application. Proper application timing in relation to the weed size is critical. You need to spray early enough so the weeds will have no more than four true leaves ensuring proper control.

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