What is in this article?:
- Lack of calcium, pigweed threaten Carolina peanuts
- Most critical nutrient
- Expectations are high
• Two factors may dampen the projected growth of peanuts in South Carolina, the availability of low cost calcium for Virginia type peanuts and the continued spread of herbicide resistant Palmer amaranth pigweed.
Most critical nutrient
In runner and Virginia type peanuts, calcium is by far the most critical nutrient for achieving high yields and grades. Low levels of calcium causes several serious production problems, including unfilled pods (pops), pod rot disease, poor grades, darkened spots in the seed and poor germination.
Virginia-type peanut varieties are less able to take up adequate calcium than runner and Spanish types. This may simply be a matter of pod size, since there is less surface area on larger pods per unit weight of nut. For runner peanuts, the critical soil test level is 600 pounds of calcium per acre, but on Virginia type peanuts, yield and grade response occurs even at a soil test of 1,000 pounds of calcium per acre.
Though glyphosate resistant pigweed isn’t routinely associated with peanut production, it is becoming an increasing problem as more and more families of herbicide — many of which are used in peanut production — fall victim to the prolific weed.
Much of South Carolina’s peanut acreage is grown in rotation with cotton or on land once used for cotton production. The combination can leave a big problem for peanut growers who once controlled the troublesome weed with herbicides to which pigweed has developed tolerance, or by chemicals put in voluntary restricted use by growers trying to save valuable weapons to fight the weed in other crops.
Pigweed is a big enough problem in South Carolina peanuts that Clemson University Peanut Specialist Jay Chapin says growers in high risk areas may want to stick with varieties that produce a lower growing bush, which will allow growers to come over the top with a wick bar to manage pigweed.
One such wicking device that has been used effectively in South Carolina is the Grassworks WeedWiper. It has a rotating drum that allows a grower to run the carpeted material very saturated, and therefore have a lot of chemical available to apply to the targeted weeds. Because the drum is rotating, target herbicides will not drip.
This machine applies chemicals to the bottom or underside of the leaves and stems, where the plants are going to be easier to kill. The drum height is adjustable, allowing growers to target pigweed that grows above the canopy of most peanut varieties.
Clemson University Weed Scientist Mike Marshall has used the machine on a number of crops with good success. Marshall says test results, using a research scale model of the commercially available machine has been good. He adds that a few farmers in South Carolina, who have used the commercial version of the machine have indicated having excellent results in controlling weed escapes in soybeans and peanuts.
He says, “The rates we’ve used are 50 percent gramoxone or paraquat and 50 percent water solution. A big advantage is that you are killing the top of the weed where seed production takes place, and with Palmer amaranth this is a big advantage because these weeds are such prolific seed producers,” Marshall notes.