Mid- And Late-Season Issues

David Jordan

DAVID JORDAN
North Carolina State University

With early season issues addressed, in July and August and into early September growers focus on controlling weed escapes, in particular annual grasses but also broadleaf weeds, foliar-feeding insects such as armyworms, tobacco budworms and corn earworms, and foliar and soilborne pathogens.

Controlling escaped grasses almost always pays for itself because of pod loss during digging. Many broadleaf weeds may be well past the size that can be controlled with herbicides, and pulling up those escapes can help not only this year but would be equally important in subsequent years.

Pay particular attention to common ragweed and Palmer amaranth. Escapes of both of these species need to be addressed, especially if you have an intense PPO herbicide regime. We don’t need biotypes of these weeds to get entrenched in fields.

In North Carolina, the threshold for foliar-feeding insects has been increased from 4 per foot of row to 8 per foot of row in July, and from 8 to 12 in August. With the presence of pyrethroid resistance and tobacco budworms, when you need to treat, the more expensive yet more effective insecticides are often the best bet for complete control.

leaf spot

Leaf spot

Leaf spot and stem rot are key issues in the Virginia-Carolina region (and elsewhere) and a well-timed, diverse fungicide program with no gaps in protection when pathogens are active is important. Healthy plants in the fall provide the greatest flexibility in digging and give us room to dig at optimum maturity.

We had a hot and dry May and that always brings concerns about spider mites. Keep an eye on fields for pockets that may develop and address those areas in a timely manner. Avoid mowing areas around fields in order to minimize movement of mites into peanut fields from weeds.

Conversely, if we have significant rain leading to robust plant growth, the plant growth regulator prohexadione calcium can be an effective option to keep excessive vine growth at bay. While expensive, in surveys of the Virginia-Carolina region, about half of the farmers make at least one application of prohexadione calcium during the growing season.

Apply at 50 percent row closure – when half of the vines from two adjacent rows are touching – and repeat the application 2-3 weeks later if peanuts begin to have new growth. It is best to error on the side of being late rather than early with the first application: we don’t need to keep peanuts from lapping rows. Always include a nitrogen solution or ammonium sulfate with this plant growth regular.

Start Planning For 2020 Now

peter dotray

PETER DOTRAY
Texas A&M AgriLife
Extension Weed Specialist

It’s July and we have seen some very successful weed management programs in peanut. One final foliar spray and an overlaying residual herbicide may be needed in some areas to complete the goal of season-long weed control.

Late-emerging weeds may not be very competitive or even impede digging, but these plants can produce hundreds to thousands of seed that will impact future growing seasons.

To recap the early 2019 growing season, most producers planted into clean beds, the first step towards successful weed management. This was achieved by tillage, use of preplant burn-down herbicides, or both.

Dinitroaniline herbicides (Sonalan, Prowl, Trifluralin), the second principle for successful weed management, were used preplant incorporated followed by an at-plant herbicide such as Valor.

After the use of an at-plant herbicide, weed management programs varied with the use of a foliar contact herbicide (Gramoxone, Cobra, Ultra Blazer) or a systemic herbicide (Cadre, Pursuit, 2,4-DB). Many growers also added a soil-active residual herbicide (Dual, Warrant, Outlook) to this postemergence application.

The abundance of clean peanut fields in July is not the result of one specific recipe to control weeds, but a diversity of herbicide programs achieving the goal of starting clean and finishing clean.

Future successful weed management programs rely in part on remembering past results — both successful and not-so-successful experiences.

Document areas in the field where weed populations and troublesome weeds are present. In 2020, these areas will need our full attention to properly manage these dense and troublesome weeds.

Rotational crops with peanut may offer alternative herbicide modes of action to help break up weed/crop associations and better manage herbicide-resistant weed populations. Be on the lookout for new or unusual weeds, and focus on accurate weed identification to aid in herbicide selection for 2020.

All the best wrapping up the 2019 growing season and starting the process to improve weed management in future growing seasons.

Disease Pressure Will Happen

Kris Balkcom

KRIS BALKCOM
Auburn University

Hopefully the drought is behind us and everyone has been receiving adequate rainfall over the past month. I know the dry weather has left us with a few challenges, mainly getting the crop in on time, having a good stand due to lack of moisture and heavy thrips pressure, which gained an advantage over us with the dry weather.

We had a difficult time knocking thrips back. The later peanuts that went in after we got some rainfall have had adequate time.

thrips injury

Thrips injury

All and all, peanuts are looking good right now because of the earlier start this year. Taking advantage of the time to plant early was as important this season because of the lack of moisture later. Last season, we were not able to be in the field because of excess moisture.

Some weed issues need to be addressed, particularly where we didn’t get any residual herbicides washed in for protection.

Hopefully you have cleaned those up and have some protection down now.

Also remember, even though disease pressure has been light so far doesn’t mean that will continue to be the case. If the high temperatures we have had continue, coupled with moisture, it will certainly increase the amount of disease pressure we could see. Therefore, be sure to try and combat that potential risk with some products washed in when you have the opportunity.

I hope everyone has a great rest of the season this year, and I look forward to seeing you in the field.

Scouting Pays

Scott Monfort

Scott Monfort
University of Georgia

The peanut crop is in peak bloom now with most of the crop between 60 and 90 days old. This is a critical time for pod set and development. There are several important things for growers to keep track of such as water needs, insects and diseases. To ensure the highest yield potential possible, each peanut field should be scouted on a weekly basis.

I know growers are extremely busy and do not have the extra time to scout their crop. This is where a county agent, consultant or crop scout can help monitor the crop and advise growers when a problem arises and whether a control measure is warranted.

This could save a grower thousands of dollars in input costs and/or loss of yield potential.

We talk a lot in meetings about how inputs affect yield. A peanut’s maximum yield potential is determined by genetics and is set before the seed is even planted. The farmer’s job is to provide an environment that allows the plant to achieve its potential without spending more money than the crop is worth.

lesser cornstalk border

Lesser cornstalk borer

Everything growers do affects how much yield and revenue are retained or reduced as a result of the cost and effectiveness of the management strategies they choose. Scouting fields on a weekly basis will provide information about what problems are developing and help determine the correct action to take to manage the situation.

Already in 2019, weekly scouting helped some growers manage lesser cornstalk borers in non-irrigated acres in southern Georgia.

This is just one instance where scouting resulted in quick identification of a problem and allowed growers to manage a pest before it severely affected the crop. Stay informed. Contact your local ag Extension agent if you need further information.