Jason Woodward covered a lot of ground in a short time — in less than an hour he touched on several cotton disease issues, discussed new options for controlling nematodes and offered some variety selection points.
The recent Red River Crops Conference in Childress, Texas, in its second year and sponsored by the Texas and Oklahoma Extension services, offered a full two days of timely information on crop production, legislation, and market outlooks.
Cotton diseases, even in the usually arid conditions of West Texas, can cause significant yield loss and harvest problems, Woodward says. Trouble can start early.
“Seedling diseases have shown up in the High Plains the last few years, even with hot, dry summers. But we’ve also seen cool, wet conditions early, at seedling emergence.”
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In 2014, conditions were improved over the previous three years, with more rainfall, mostly to the east of Lubbock. Temperatures also moderated. “Some of the hotter days occurred in May, so we saw less disease early in the season,” Woodward says. “We did have problems when the temperatures dipped, usually accompanied by rainfall.”
Planting problems may have contributed to stand loss. “Planting too deep increases stress on seedlings and may result in poorly-developed or rotted root systems. The pathogens that cause disease can easily overtake stressed plants.”
Also, lower germination, seed rot, and preemergence and postemergence damping off resulted in stand losses.
“Seedling diseases are favored by cool, wet conditions,” Woodward says. Treated seed, including fungicide treatments, may help reduce vulnerability to these diseases.
The lower price for cotton might discourage growers from using a “premium fungicide program,” he says, “but, if producers decide to decrease planting rates to save money, they might consider putting some of the savings back into premium fungicides, especially when planting early or into cooler soils.”
He also discussed cotton root rot, not an issue statewide, but a potentially devastating one in some parts of the Rolling Plains and other areas with heavy soils.
A recent emergency exemption for Topguard fungicide has provided cotton farmers at least the opportunity to control a disease that had baffled researchers for 100 years. Application of Topguard with either a T-band or Y- split method resulted in a significant reduction in disease infection and also improved harvest efficiency.
Phytotoxicity of the material has been a question, especially when rainfall follows closely behind application, Woodward says. Toxicity behind the T-band was negligible, and with the Y-split, damage was “rate dependent. A lower rate meant less stand loss.”
Research and Extension specialists are looking at other application methods, including knifing-in Topguard at various depths — 6 inches, 8 inches, and 10 inches. “When we knock off the 3-inch bed, we get 3-inch, 5-inch, and 7-inch depths. We observed no phytotoxicity and a significant reduction in root rot,” Woodward says.
A new formulation may be available soon. “We also are interested in more studies to reduce potential for phytotoxicity,” he says. Studies may include research on moisture management after application.
Root-knot nematode infestation is another factor for potentially significant cotton yield loss in some locations. “Infected plants may exhibit nutrient deficiency symptoms,” Woodward says. “Nematodes feed on and create galls on the roots and prevent the plant from picking up moisture and nutrients.”
Chemical control options are limited. “We now have some varietal resistance,” he says. Susceptible varieties allow nematodes to reproduce on the root systems and provide potential for significant losses. Resistant varieties limit nematode reproduction.
Several varieties, including Stoneville 5458 and 4946, FiberMax 2011, Deltapine 1454, and Phytogen 427 and 417, show good resistance. Others, such as NexGen 1511, may not be resistant, but perform well, even with nematode infestations. “In high infestation fields, resistant varieties would be best,” he says.
Rotation and irrigation also affect nematode damage. Cotton followed by wheat, then summer fallow, is a good option. “Also, with more irrigation, we see less damage,” Woodward says. “Stress under lower irrigation results in more nematode damage. Irrigation develops better root systems allowing plants to overcome higher nematode populations.”
Nematodes also point out the necessity of following a comprehensive cotton management program. Weed control may be a key step in keeping the pests at bay. Russian thistle, for instance, is a host for root-knot nematode.
“We’ve pulled weeds and identified galling, similar to root-knot nematode signs on cotton. This weed is a suitable host. I’ve also seen galls on pigweed and morningglory. If producers neglect weed management, it could negate nematode management practices. Also, if producers rotate cotton with a wheat and summer fallow program, they need to manage weeds in fallowed wheat.”
Discussing cotton foliar diseases, Woodward says, “Leaf spot occurs late in the season and is usually not a concern. If it comes on earlier it could cause problems.” Leaf spot could be linked to potassium deficiency.
Bacterial blight is something “we deal with every year,” he says. “Dry, cool winters allow for survival of the causal agent. We can see defoliation from bacterial blight, and it can be significant enough to affect yield. There is also potential to infect bolls and stain lint.”
Verticillium wilt also infects Southwest cotton, especially in high-yield environments. Again, Woodward suggests producers who may be cutting seeding rates to reduce costs consider investing in a premium fungicide treatment to help manage Verticillium wilt.
“Fungicides have no direct effect on the fungus. Studies have shown that reduced seeding rates increase the severity of the disease. Producers may negate the impact of the disease by optimizing stands with a premium fungicide.”
Cotton farmers should take a hard look at variety selection, Woodward says, and choose varieties that perform in the top tier in Verticillium tests.