Plan to mitigate crop diseases
Crop diseases reduce yield, but with the right planning, farmers can lessen their effect and realize the full potential of their crops.
Jordan Bassler, agronomy leader at Seed Consultants in Washington Courthouse, Ohio, presented at the recent A.N. Martin Open House.
“Red crown rot is big in soybeans in the South,” Bassler said, and not much in the Northeast. But when red crown appears, it’s important to treat it before it spreads.
Red crown rot (Calonectria ilicicola) is a fungus related to black rot in peanuts. Its wide array of hosts include acacia, kiwifruit, papaya, holly, oleander, blueberry, soybeans and more. The disease can survive in soil for several years and colonize in soybean roots.
In soybeans, the fungus moves up the plant stem from the roots and accumulates in the leaves. The ideal soil temperature for its development is 77º – 86º F.
“Infections can occur during the seedling stage soon after germination,” Bassler said. “Early infections generally result in the most severe symptoms. It can cause a whole gamut of symptoms.”
These include necrosis of the leaves; reddish lower stems and roots; reddish-orange, spherical perithecia on the lower stem and root; root rot; and patch distribution in the field.
Farmers will observe “leaf death between the veins like sudden death syndrome,” Bassler said.
The disease process mimics sudden death syndrome, but that has blue sporulation on the taproot and a chocolate brown-discolored vascular system in the lower stem and root.
Red crown rot moves any way that soil can move, as it’s a soil-borne disease. It moves with the flow of water, on plant debris, via animal movement and when transported by equipment. It’s wise to use equipment last on a field with red crown rot and then cleaning it well afterwards.
Bassler advised rotating crops with non-host crops for multiple years so that red crown rot lacks a host. Farmers can help reduce the negative effects on yield of red crown rot by improving their overall management, such as managing soybean cyst nematode and other stresses; selecting the right planting date, keeping in mind the ideal soil temperature for infection; researching fungicide seed treatments; and avoiding planting super-susceptible varieties.
Unfortunately, few seed treatments list efficacy against red crown rot. There’s limited public information on fungicide seed treatments that prevent it.
The effect on yield is stark. Bassler said that measured yield components on symptomatic vs. asymptomatic plants show that the plant weight, number of pods and number of seeds is more than halved among the symptomatic plants on average.
“Double-cropped fields are affected more severely than full-season fields,” Bassler said. “June/July planting dates are more susceptible than April/May planting dates.”
The cooler season planting means that soil temperature is not ideal for development of red crown rot.
Bassler also spoke about a soybean serine acetyltransferase (SAT) trial.
“Easly season diseases are the number one cause of replant decisions,” Bassler said. These include Pythium Fusarium, Phytophthora and Rhizoctonia.
The trial looked at Pythium, primarily occurring in soybeans in low-lying, waterlogged areas of fields. These diseases overwinter in corn and soybean residue and cause seeds to rot. Seedlings will show water-soaked lesions.
Fusarium, another cold soil temperature disease, infects soybean seedlings and causes a stunted appearance. The roots remain compromised during wet conditions and symptoms will often manifest during dry weather.
Phytophthora is a warm soil temperature disease that needs wet soil. The seeds rot before emergence and lesions will girdle the stem on larger seedlings.
Rhizoctonia is a warm soil temperature disease that prefers dry soil. It can affect soybeans and corn.
In a trial comparing an untreated control plot with areas treated with LumiGEN FST/IST and Lumidapt™, an on-seed biologic that provides micronutrients to boost yield, researchers found LumiGEN boosted yield by 4.2 bushels/ acre and when used with seeds treated with Lumidapt, the variety provided an additional 5.7 bushels/acre.
Bassler said research for LumiGEN will continue and Lumidapt will become another tool farmers can use to increase yields. His photos of plots treated with LumiGEN showed a marked difference compared with non-treated plots. But Lumidapt’s results are more subtle.
“Visually, you won’t see a difference starting out until you dig up a plant,” Bassler said. “You’ll see an increased root mass and growth.”
Bassler encouraged farmers to look at fungicides by mode of action. “This is key in selecting fungicides and is critical for resistance management,” he said.
Formulation can include suspension concentrate and emulsifiable concentrate. Farmers need to pay attention to the range of diseases controlled and whether it’s systemic or contact protection. Residual activity also matters so farmers can plan for any needed reapplication. The application flexibility relates to tank mix compatibility re-entry interval and pre-harvest interval.
Timing of the application should be considered as well.
“Glyphosate doesn’t work as well as it’s used over and over until resistance builds up,” Bassler said.
Resistance also builds as farmers plant the same crops (like corn after corn) and use the same products year after year. Bassler noted that resistance can be abrupt, caused by a single gene mutation that leads to rapid, complete loss of control, or gradual after multiple gene mutations slowly reduce sensitivity.
In general, when applying fungicide, “don’t skimp on those rates. And plant more tolerant hybrids.”
