PPOresistant Palmer amaranth has popped up in North Carolina which is a major concern for corn growers

PPO-resistant Palmer amaranth has popped up in North Carolina, which is a major concern for corn growers.

PPO inhibitors shortcomings prompt concerns

Palmer amaranth continues to rear its ugly head in North Carolina, and stink bugs remain a nemesis in corn. N.C. State is investigating populations of pigweed that survived applications of Liberty in North Carolina this year.

“PPO inhibitors don’t work for us on a wide scale, so we need to start thinking about changing what we are doing and be more proactive,” said Wes Everman, North Carolina State Extension weed specialist.

PPO-resistant Palmer amaranth has popped up in North Carolina, which is a major concern, said Everman, at the Blackland Farm Managers tour Aug. 5 held at Circle Grove Seeds and Haslin Farms in Belhaven, N.C.

"We don’t have a new mode of action that is going to bail us out,” he said. “What we have is what’s going to be in our arsenal for the next 10, maybe 15 years. Liberty, dicamba and 2,4-D are our three options. They have 2,4-D-resistant water hemp in the Midwest, so we know it’s a matter of time before we see 2,4-D resistant palmer if we don’t protect it.”

In the meantime, N.C. State is investigating populations of pigweed that survived applications of the herbicide Liberty in North Carolina this year. “We’re not ready to say we have Liberty-resistant pigweed, but we are looking at it,” Everman said.

Crop rotation of corn with soybeans, incorporating multiple herbicides, proactive scouting and hand removal of weeds are critical tools for Palmer control, he stressed. Post-harvest management is vital.

“We have to start looking at the system and how we can incorporate herbicide-resistant weed management in a whole system not just year to year. We have to quit  looking at what  am I going to do right now and say what am I going to do next year and the year after,” Everman said.

Stink bug problems

In addition, stink bugs are becoming a growing problem in eastern North Carolina corn with the pest developing in both wheat adjacent to corn as well as in weeds that border corn fields, said Dominic Reisig, N.C. State Extension entomologist.

Reisig conducted a test this year where three gallons of pesticide were sprayed aerially over corn and he found that the applications were essentially ineffective in controlling stink bugs because the bugs were hiding down low in the canopies of the corn plants and the insecticides didn’t reach them.

Reisig said the key is to determine when stink bugs move from wheat to corn which will hopefully allow for more effective insecticide treatments. Scouting is critical, he said. “There are no shortcuts for managing stink bugs in corn,” he stressed.

Fertilizer response

Carl Crozier, N.C. State Extension soil fertility management specialist, stressed the importance of soil tests to diagnose nutrient deficiency in corn with soil tests. Crozier said it is critical to properly interpret the soil test index numbers.

“We have a philosophy in how we interpret these soil test results,” he explained. “And the general principle is the lower that number is, the more likely we think you are to get a fertilizer response. Once that index goes high enough, we think whether or not you put fertilizer out or not, you’re not going to get any extra yield response because something besides fertility is limiting yields.”

Crozier recommends tissue analysis for each crop to determine if nutrient concentrations are at an optimal range. He also recommends grids sampling with each sample representing a smaller area to better determine the actual fertility in each part of a field. A more aggressive fertility management approach is to look at what the yield map shows, Crozier said.

If the yield map shows a low yield in a certain part of the field with the highest soil test index, something else besides fertility may be limiting yields and you are building up extra fertilizer that you don’t need. If the yield map shows you are low on yields because you are low on nutrients, you may the apply more fertilizer because of leaching.

Farmers may want to add extra fertilizer to increase residual nitrogen in their corn when fertilizer prices fluctuate and an application is more affordable, Crozier said. “For high yield systems at some point more fertilizer has to go into that system. You ca get to those higher yields by adding more fertilizer to the system,” he said.

This year’s Blackland Farm Managers Tour drew a crowd of 450 people. It is considered the preeminent crop field day in North Carolina.

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