By Jeff Burbrink
Extension Educator, Purdue Extension Elkhart County
ELKHART — There are two major issues this fall: tar spot affecting the stalks on corn stalks, and the moving of herbicide-resistant weed seeds from one field to the next.
It has become painfully obvious that many corn fields in the area were hit hard by tar spot. While the dry weather the past few weeks was one reason the corn browned so early, tar spot accelerated the drying out process even more.
One farmer told me last week, “the tops of the corn are just broken off on many of these varieties,” referring to the common sight of stalks snapped off a foot or two below the tassel, and the field taking on a ragged appearance. I am hearing yield estimates of 100-130 bushels per acre in fields that typically average 200-250 bushels the past few years.
Tar spot takes yield away in two ways. First, there is the reduction in photosynthesis caused by the lesions and death of the leaves. The leaf damage is something we can manage with timely applications of fungicides before the damage is spread through the field. The second yield-killer is the damage to the stalk, making it more brittle and less likely to withstand wind, storms or even the gathering chains on the combine.
Like many diseases, if tar spot is not suppressed well in the leaf lesion stage, it will probably weaken the stalk and cause further losses in the fall. Those fields with that raggedy appearance should be among the first to be harvested. Take note of which varieties stood up to tar spot, and those that collapsed under the disease pressure. If you have tar spot in 2021, it will be there in 2022 and beyond most likely.
The other concern is weed seed being transferred from field to field by harvest equipment. One grower told me about a field that had no waterhemp in 2020. In 2021, he found waterhemp growing in the end rows where the picker first opened the field in 2020. He’s confident the seed came from the previous field, where waterhemp had just got a start a few years back.
In this era of herbicide-resistant weeds like waterhemp, marestail and Palmer amaranth, cleaning the combine, picker or other dust collecting equipment before it moves to the next field may slow the spread of these awful weeds, and maybe save you money on high-powered herbicides for a year or two more.
There are farmers who have made combine cleaning between fields a part of their routine. They use leaf blowers to blow the dust and plant residue off the combine, which also reduces the risk of fire. They empty debris traps between fields, and they use sawdust to clean the grain pathway of debris. Some of these folks even capture the dust and dirt and dispose of it, rather than leaving it in the field.