Tall waterhemp and Palmer amaranth are two weeds glyphosate resistant weeds found in New York. These are relatively new weeds that are slowly spreading across the state. Weed seed movement is the primary way weeds will spread across the field, farm, county, and state. Weed seeds can be spread by wildlife, soil movement (i.e. erosion), wind dispersal and equipment (i.e. tillage, planting and harvest).
Possible ways tall waterhemp and Palmer amaranth came to NYS include waterfowl, whole cottonseed used in dairy rations, seed mixes (pollinator and landscape seed), harvest equipment (combines). Purchasing used combines from other states is one of the more likely methods of introducing resistant tall waterhemp and palmer amaranth on the farm.
A sound integrated weed management practices includes mechanical, cultural, chemical, biological, and prevention. Prevention is the most overlooked weed management strategy. The easiest way to control weeds is to not let them get established on your farm or in your field. Cleaning equipment to prevent the spread of weed seeds is an important weed control strategy. Both tall waterhemp and Palmer amaranth can produce over 1 million seeds per plant. It does not take very many plants to become a major problem in a field.
To demonstrate how weed seeds can be moved via combines, Cornell Cooperative Extension North Country Regional Ag Team Field Crop Specialists worked with a grower that had recently purchased a used combine from Illinois. It has been previously documented that combines can contain approximately 150 pounds of biomaterial (chaff, grain, weed seed). Prior to its use on the farm, we did a thorough cleaning of the combine that the grower had purchased from out of state. We retained all the biomaterial that we could to look for weed seeds. After cleaning the combine, the biomaterial was screened multiple times and weed seeds were sorted out individually by hand. Approximately 97 percent of the weed seeds collected from the combine were tall waterhemp, a weed currently not found on this grower’s farm.
Cornell Cooperative Extension Field Crop Specialists sent the collected weed seeds to Cornell AgriTech in Geneva. Dr. Bryan Brown, New York State IPM Program, and Dr. Lynn Sosnoskie, assistant professor in the School of Integrative Plant Science at Cornell AgriTech, planted the weed seeds in the greenhouse and screened this population of tall waterhemp for herbicide resistance. They sprayed herbicides from six different classes and found that this population of tall waterhemp was resistant to four of the six herbicide classes used.
The results of this project showed how troublesome weeds, such as tall waterhemp, can be brought to farms via harvest equipment purchased from other areas of the country. If growers spend the time to prevent the movement of seeds by cleaning combines prior to using them it will reduce the likelihood of these resistant weeds becoming a problem in the future. Growers must be cautious with any purchase of used harvest equipment from areas containing herbicide resistant weeds. Once tall waterhemp and Palmer amaranth become established on a farm weed control costs will be increased.