Managing Weeds With PP, PPI And Pre Herbicides

• By Emi Kimura, James Grichar, Pete Dotray and Josh McGinty, Texas A&M AgriLife Extension •

weed sprayerBest management practices for peanut production include effective season-long weed management. The four weed management principles in peanut production are:

1. Start clean.

2. Use residual herbicides.

3. Be timely with postemergence applications.

4. Know your weeds.

Early season weed management is most important and should result in easier weed control later in the season. There are five critical herbicide application timings in peanut production. These application timings include preplant burndown, preplant incorporated, preemergence, early postemergence and postemergence. Yield losses are minimized when peanuts are free of weed competition for the first four to six weeks after planting.

The use of PP, PPI and Pre herbicides are critically important for minimizing weed competition during the early season. April is a good time for planning and applying PP and PPI herbicides in your peanut fields while Pre herbicide applications are made at planting. Early post timing is 10 to 20 days after planting, with postemergence 20 to 45 days after planting.

Preplant Burndown

Early emerging weeds, such as Russian thistle and kochia, can be controlled by tillage or use of burndown herbicides. One of the strengths of paraquat is control of Russian thistle, and glyphosate is effective on a broad spectrum of annual and perennial grass and broadleaf weeds.

Preplant Incorporated

Preplant incorporated herbicides labeled for peanut include ethalfluralin, pendimethalin and trifluralin. These dinitroaniline herbicides, also known as yellow herbicides, are effective on annual grasses and small-seeded broadleaf weeds such as Palmer amaranth, Russian thistle and kochia. However, these herbicides are ineffective at controlling large-seeded broadleaf weeds such as cocklebur, sunflowers, and both yellow and purple sedges. The use of a Pre herbicide will enhance control of some of these weeds.

Read the label carefully for recommendations regarding effective incorporation methods for PPI herbicides. If incorporation is too deep and peanuts are planted too shallow, roots from planted seed will go through the treated soil, which can result in stunting.

Preemergent Herbicides

The use of a Pre herbicide can be effective in controlling annual broadleaf and sedge weeds. There are several options for Pre herbicides in peanut. They are flumioxazin, S-metolachlor, dimethenamid, acetochlor and imazethapyr.

Pre herbicides must be applied and activated before weed emergence. Additionally, some of the Pre herbicides must be applied prior to peanut emergence to avoid crop injury. Please read labels carefully for incorporation methods (irrigation, mechanical), application rates, application timing, and grazing or feeding restrictions.

Flumioxazin should be applied prior to planting and up to two days after planting but before peanut emergence. It provides four to six weeks of residual activity for controlling Palmar amaranth, golden crownbeard, morningglory species and other weeds. Crop injury can occur if flumioxazin is applied three days after planting. Severe stunting can occur if flumioxazin is applied alone or in combination with S-metolachlor under cold, wet soils or water-logged conditions, and peanuts may not recover during the growing season.

Acetochlor and dimethenamid provide good residual control of grass weeds and small-seeded broadleaf weeds, and can control ALS-resistant Palmer amaranth.

Always Read The Label

It is important to read the label carefully, especially for application rates based on your soil type, feeding restrictions, rain-free periods, rotation restrictions, herbicide groups and other instructions.