A group of us toured some Palmer amaranth and waterhemp infested farms on Monday, August 23. We started off at the Landisville Research Farm and headed south. We revisited some farms that we first visited in the fall of 2014 and although the problem still exists, these farmers are proactively trying to manage it.
On an Amish farm near Quarryville, the farmer was well aware of Palmer amaranth and trying hard to make sure that it was contained. He mentioned that he had at least three of his boys out rogueing some of this ields and was trying hard to make sure it did not set seed. At the same time, it was disappointing to see that the Palmer was persisting and will likely be successful in both his corn and alfalfa (see first image).
A perennial forage like alfalfa that allows mowing is certainly better than trying to manage it in soybean, but it is clear that this will not be the answer alone for this resilient invasive weed. We visited another farm where the soybeans were almost chest high, but the pigweeds were two or more feet taller than the soybeans.
The farmer had hired a crew to walk his fields a few weeks back to pull the weeds. Although they had missed some of the pigweeds, it was certainly better than it would have been and hopefully the crew will return and continue the job using some of our “pigweed bags” once they can get back into the field.
From Lancaster County, we traveled West and North to Berks County to an area where Palmer amaranth and waterhemp have been expanding over the last three years. We visited some fields near Robesonia observing a number of problem fields. On one farm, waterhemp was quite abundant and you could see the pattern where the combine harvest from last season helped distribute the seeds (see second image).
We were told that the farmer made three herbicide applications to the problem fields (PRE and two POST applications) and you could see where the POST contact herbicide had killed the apical meristem, but the plants had recovered and were now flowering. At a meeting we attended last week in Beltsville MD, some colleagues from the Midwest talked about multiple herbicide resistance in waterhemp in parts of the Corn Belt.
Resistance to the PPO (Group 14) herbicides is becoming much more frequent and that is one of the primary tactics used for control in soybean.
It is obvious that management on some farms is not working and the results will likely spread to neighboring fields, farms, townships, and counties. Importing weed seeds onto farms in feed, hay, and other commodities can be a serious problem. Once introduced, spreading seeds through equipment and particularly during combine harvest will quickly move these pigweeds into new fields and on to neighboring farms.
Herbicide Resistance Info
Management needs to be more than simply adding additional herbicides to the regime. In the Southern US where Palmer amaranth is widely distributed, growers are looking at alternatives and in particular options for controlling weed seeds during or after cash crop harvest.
Scientists at the University of Arkansas and other institutions are testing “harvest weed seed control” (HWSC) tactics for their effectiveness in the control of invasive pigweeds and other problem weeds. The management tactics being tested include using chaff carts, narrow-windrow burning, and using the Harrington Seed Destructor (HSD) developed in Australia.
The HSD pulverizes the weed seeds that remain on the plants at harvest time (see third image). We visited with USDA-ARS scientists at Beltsville, MD where they are beginning to test the HSD. Two of these machines currently exist at USDA research labs and the Arkansas team is anxiously awaiting the arrival of an HSD component that will be integrated into a conventional combine.
Preliminary results from Australia show that 95% of weeds seeds were destroyed with the HSD. We will try to keep you abreast of HWSC development as our invasive pigweed problems continue to develop.