Postemergence Herbicide Options

peter dotray

PETER DOTRAY
Texas A&M AgriLife
Extension Weed Specialist

One of the keys to success in peanut production is effective early season weed control. Peanut fields must be kept clean for the first 4 to 6 weeks to maximize yields. This is accomplished by the effective use of preplant burndown herbicides or tillage before planting, the use of Prowl, Sonalan, trifluralin preplant followed by incorporation either mechanical or irrigation, use of Valor, Dual Magnum and Strongarm (where labeled) preemergence, and the use of Gramoxone from ground crack to 28 days after cracking.

Success of preplant herbicides is largely based on thorough incorporation and preemergence herbicides on timely rainfall or overhead irrigation to effectively activate these herbicides. In time, expect these products to give way to weed escapes and be prepared with timely postemergence applications for full-season weed control.

Basagran, Cobra and Ultra Blazer are options for use early postemergence. Basagran has activity on common cocklebur, annual sunflowers and yellow nutsedge; whereas, Ultra Blazer and Cobra are effective on Palmer amaranth, annual morningglory and other annual broadleaf weeds. Weed size and health can impact the efficacy of these contact-type herbicides. As weed size increases, herbicide activity decreases. With no residual activity, thorough spray coverage is important.

Storm, a prepackaged mixture of Basagran and Ultra Blazer, may be used to control a wide range of small and actively growing annual broadleaf weeds. All of these herbicides need a spray additive (e.g. a crop oil concentrate) for maximum activity. Herbicide options to control grassy weeds include Select and Poast.

sprayerCadre and Pursuit have good activity on many annual broadleaf and grass weeds, and nutsedge. These herbicides have good foliar and soil activity. One of the major disadvantages of these herbicides is the 18-month rotation restriction following application before cotton and grain sorghum may be planted. The development of weeds resistant to Cadre and Pursuit has increased concern across the peanut belt.

2,4-DB (Butyrac or Butoxone) is also an option for use postemergence, but extreme care must be taken when using this herbicide. 2,4-DB has good activity on most annual broadleaf weeds including morningglory and sunflower and larger and tough-to-control perennial weeds, such as silverleaf nightshade (whiteweed). The use of crop oil with 2,4-DB will increase activity, but will also enhance phenoxy-type symptomology in peanut.

Previous research suggests that this injury will not result in yield loss. 2,4-DB may be tankmixed with other herbicides to broaden the spectrum of weeds controlled. Proper tank clean out and drift reduction must be a priority when selecting this herbicide. Even better, designate a separate sprayer for use of all phenoxy-type herbicides.

Preparing For Planting: Part II

Scott Monfort

Scott Monfort
University of Georgia

April is upon us, and many growers are busy preparing ground for planting. Growers need to be aware of seed quality and the weather/soil conditions at planting in order to achieve adequate plant stand establishment. Stand establishment sets the overall yield potential for every peanut field. University of Georgia Extension recommends growers plant 6 seed per foot to obtain, at least, 4 uniform plants per foot.

This will aid in the reduction of Tomato Spotted Wilt Virus (TSWV) incidence and maintain high yield potential. It is important for growers to know (or ask for) the percent germination of the seed they are planting so seeding rates can be adjusted appropriately.

Please follow your local weather conditions as you approach planting. The average daily temperature at the 4-inch soil depth needs to be 68 degrees F for at least 3 days with no cold temperatures forecasted the week after planting.

The only exception is if it is a non-irrigated field where soil temperatures are 65 to 67 degrees F and there is adequate soil moisture but no rainfall in the forecast. Please remember the closer to 68 degrees, the faster the emergence rate. Remember, Easter is on April 21 this year, which could mean a late cold snap. This may not be scientifically accurate, but my grandfather always said it was true.

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Moisture is another important factor to consider. Too little or too much can lead to stand issues. Also, do not plant in dry-hot soils and then irrigate afterwards. It can lead to erratic germination and emergence. In these situations, always irrigate 0.25 to 0.5 inches before you plant and then again afterwards to activate herbicides. Hopefully, growers will have adequate moisture to plant non-irrigated fields and receive a shower shortly after planting to activate herbicides.

Herbicide injury (typically Valor) is always a topic of conversation this time of year. Several people have asked, “Do I need Valor?” or “Are there ways to minimize injury?” The answer is “Yes” to both questions. Eric Prostko consistently says, “The key to managing weeds is to start clean and use the UGA recommended herbicide programs.”

With this in mind, one of the key components is Valor. It provides the initial protective barrier needed to allow peanut plants time to emerge and cover the ground before weeds have the opportunity to become a problem.

Growers can minimize Valor injury by:

peanuts cover crop■ Planting high-quality seed (germination and vigor). Seed quality is important in 2019. Find out the percent germination of peanut seed.

■ Planting into good moisture and temperature allowing the seed the best opportunity to germinate and emerge quickly.

■ Planting peanuts at the correct depth of at least 1.5 inches deep. Planting shallower can increase risk of Valor injury along with germination issues if soil dries out too quickly.

■ Applying Valor no later than 2 days after planting. The risk of Valor injury goes up significantly the closer Valor is applied to peanut emergence.

■ Irrigating as soon as possible behind the Valor application to activate herbicide and reduce injury. Valor injury can still occur after a hard rain during cracking and emergence even though a field was irrigated after application.

■ Not irrigating during cracking and emergence unless the fields are hot and dry and need irrigation to ensure a good stand.

Typically, the lack of moisture can result in more stand loss than the loss from Valor injury.

These are critical components in getting the crop started on the right foot. Call your county agent if you have any questions regarding any of the information discussed above or if you need any further information.

Protection Against Thrips

David Jordan

DAVID JORDAN
North Carolina State University

By this point in the spring, decisions on acreage and field selection have likely already been made. Past production history in these fields can inform us on what to expect in terms of presence of pests and how we need to keep injury caused by these pests below economic injury levels.

In the Virginia-Carolina region, it is almost guaranteed that weed and thrips populations will be well above economic injury levels if we don’t treat for these. In fact, it often takes more than one application of pesticides to suppress these pests.

For weeds, overlapping applications of residual herbicides is recommended within the first month of the season — preplant burndown or preplant incorporated, preemergence right after planting, early postemergence with paraquat plus Basagran — to make sure the impact of the first flush of weeds is minimized.

Because most growers in the Virginia-Carolina region are dryland producers, overlapping residuals or making multiple applications of herbicides so that adequate concentrations of residual herbicides are maintained in the soil stacks things in our favor for getting activating rainfall.

The first weed flush after conventional tillage is often the biggest if we don’t disturb the soil later in the season with cultivation. Having adequate residual herbicide in the soil for suppression of that flush is important.

Likewise, peanuts emerging in May in the Virginia-Carolina region can grow slowly in some years and this leaves plants vulnerable to thrips feeding and possible reductions in yield. Thrips can hammer away at yield potential if left uncontrolled, and they can also transmit tomato spotted virus to more plants in the field.

Systemic insecticides are a must to protect yields in our neck of the woods. Suppression of both weeds and thrips serve as a foundation for success as the season progresses. We currently have a good assortment of products to use for both groups of pests.

No matter what products you use or what your expectations are on performance, scout often in the early stages of the growth cycle so that follow up treatments can be made in a timely manner if needed. Getting behind, both for the peanut crop and the grower, makes for a long and challenging season.

Know The Germ Percentage

Kris Balkcom

Kris Balkcom
Auburn University

Spring is here and as I write this, I don’t know how close we are to planting time. However, we were predicted to have an early spring and it has been a warm mild winter. Therefore, we are probably looking to plant some peanuts very soon depending on conditions.

I have some concerns as we enter the 2019 planting season. Economics being the first one. We don’t need to plant a lot of peanuts at the current price. Hopefully, cotton will come around and rally to give us a leg to stand on. Second, the warm winter we’ve had typically brings on increased thrips pressure.

That is also alarming since we still plant the majority of the crop in Georgia-06G. We have had this variety for 13 years now, and I feel we are at an increased risk of it being vulnerable to circumstances.

The weather pattern is another concern. We have been wet for over a year now. We know that this is likely to change at some point. Therefore, timing is critical to land preparation and conserving soil moisture for planting. We need to be aggressive in having the crop ready to plant as early as we can due to the unknowns.

Last year showed us that even though it was just mid-May, we didn’t get an opportunity to plant again for about two and a half weeks.

The last several years have proven that April peanuts are far better than June-planted peanuts. I am not saying that you have to plant the entire crop in April, but it’s a means of spreading risk. If you’re a large producer, you need to be ready to start planting in April, whereas if you’re a small producer, you can plant at more of an opportune time.

Increased nematode pressure is also a concern because of the wet and warm winter. I would encourage those who have peanut root-knot nematodes to consider planting early. TifNV-HiOL is a new variety that is resistant to root-knot as well as Georgia-14N that we have had for a few years.

Both varieties have great resistance to TSWV in addition to a good disease packages.
Take the time to look at the Peanut Rx. This will give you some idea about the amount of risk with each variety as they relate to TSWV, leaf spot and soilborne disease. Lastly, seed quality is a concern because of conditions during harvest this past year.

By law, seed peanuts only have to be 75 percent germination or above. I would suggest that you know exactly the germination of your seed. That way if you have some lots that are 90 percent and some that are 78 percent, you can plant the 90 percent first, when conditions may not be perfect to ensure yourself a better stand, then plant the 78 percent germination seed later, when conditions have warmed up and are more favorable resulting in a chance for a better stand.