Each season, row-crop growers in the Southeast go to great effort and great expense to reduce losses to diseases and nematodes. One of the most important things I do provide, through Extension programming, recommendations to best integrate varieties, fungicides, nematicides and cultural practices to minimize losses.  

Perhaps the best example of such is Peanut Rx and associated “prescription” fungicide programs. I am grateful that there are companies that sell products to protect against damage from diseases and nematodes.

I sometimes feel sorry for the sales reps facing angry growers who are disappointed by the amount of disease damage they perceive in their field. Sometimes, damage is inevitable, despite best efforts, and minor damage may not affect profitability. 

Tomato spotted wilt 

The complaint is, “I followed Peanut Rx like you told me to do, and I STILL have tomato spotted wilt in my peanuts. Why is that?” 

Short of having a peanut variety that is completely resistant to the tomato spotted wilt virus, there is going to be some spotted wilt disease in every peanut field in the Southeast. The amount of spotted wilt in any field is dependent upon the overall threat from viruliferous thrips in a season and the steps that were taken to minimize risk, with particular emphasis on variety, planting date, plant populations and selection of what to put in-furrow. What seems like “too much spotted wilt” would become more acceptable if a grower could see how much wilt there would have been had he or she NOT followed Peanut Rx.   

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Leaf spot diseases   

Early leaf spot and late leaf spot are two of the most common and important diseases affecting our peanut crop. Many growers will apply fungicides up to eight times this season to manage these diseases. They are understandably concerned if leaf spot is found in the field.   

Significant premature defoliation reduces the strength of the pegs that attach the pods to the plants.  Weakened pegs can result in digging losses at harvest. Most fungicide programs reduce leaf spot to where symptoms are insignificant.   

However, there are times, for example, when a variety is more susceptible, or when peanuts are planted too often in a field, or when weather is extremely favorable for disease, that defoliation does occur. Growers can find solace in the fact that our current varieties can withstand some defoliation at harvest without significant yield loss. 

Southern stem rot/white mold   

Managing this disease can be quite difficult, more difficult than managing leaf spot diseases.  Management of white mold requires not only proper application timing with use of an appropriate product at an appropriate rate, but also rain, irrigation, increased spray volume, or by spraying at night to move the product to the crown of the. Despite a grower’s best efforts, some white mold is likely to appear in most fields every year.   

The indication that the management program (the combination of timing, fungicide and application method) is working is that any “hits” of white mold are contained to about the size of a dinner plate.   

Indications that a management program is not working show when the disease expands beyond individual plants and spreads down the row. When such occurs, it is extremely important that a grower re-evaluate and work to contain the disease.  Such may require switching products, adjusting rates, and/or trying to improve movement of the fungicide to the canopy of the plant. 

Root-knot nematodes   

Planting varieties that have resistance to the peanut root-knot nematode is the most effective tool for reducing losses to this difficult-to-manage pest. Even when resistant varieties are planted, it is possible that a very small amount of damage will still be observed in the field, though our resistant peanut varieties, to include ‘Georgia-14N’, ‘TifNV-High O/L’, and more recently ‘TifNV-HG’, are nearly immune.   

Growers who plant a susceptible variety, for example ‘Georgia-06G, WILL see nematode damage in an infested field (stunting, gall on roots, pegs and pods) no matter which nematicide or combination of nematicides is used.  In such instance, the best the grower can do it to choose the nematicide and rate of the nematicide most appropriate for the size of the nematode population in the field and manage the crop as effectively as possible to reduce stress already present from a compromised root system. 

There have been many times when I am called to the field because a grower is despondent at the amount of disease seen. Sometimes, as we look at the field together, the grower realizes it is not as bad as it first seemed, or that things can still be done to protect the crop. Realistic expectations and careful observations can make all the difference in a crop this season. 

Kemerait is a plant pathologist with the University of Georgia and regular columnist for Southeast Farm Press.