Josh Putman, Field Crops Specialist, CCE SWNY Dairy, Livestock, and Field Crops Team Tall waterhemp is one of the most problematic weed species throughout the Midwest and has now arrived and spread to eight counties in Upstate New York. Waterhemp can spread from field-to-field and farm-to-farm on equipment, clothing, application equipment, or via water from over flooded ditches and rivers. Following a recent field day event we wanted to demonstrate the amount of weed seed that could travel back with you. Boots that were considered “clean” were not as clean as we had thought (Figure 1). A knife was used to clean the boots and break up any hard clots that were present. Once the boots were clean, tweezers were used to separate the weed seeds from the dirt (Figure 2). The pigweed/waterhemp seed was then separated from other weed seeds that were present, and pigweed seeds were counted (Figure 3). The clods of dirt were also checked, and one pigweed seed was found stuck to a clay particle (Figure 4). An estimate of a 3 year establishment of waterhemp assuming 50% of the seeds were waterhemp and 100% were waterhemp was then calculated, respectively. The calculations are seen below:16 pigweed seeds + 1 pigweed seed hiding in soil = 17 pigweed seeds from 2 boots. Assuming only half of those are waterhemp and it can produce 250,000 seeds per female plant: 17/2 = 8.5 X 250,000 = 2.125 million seeds the following year in a field. Assuming every seed on the bottom of the boots are waterhemp: 17 X 250,000 = 4.250 million seeds the following year. Assuming 75% survival rate and reproduction in year 2: 4.250 million X 75% = 3.1875 million plants X 250,000 seeds per plant = |**796,875,000,000 seeds going into the soil in year 3 (potentially) In conclusion, correct and early identification is very important; learn the correct characteristics of the plants (Figure 5) and seeds. Proper cleaning and sanitation of equipment, clothing, and vehicles can help prevent spreading. Intense management and continuous scouting are vital to eradication of this weed species. Mechanical control such as plowing can bury the seed deep which might decrease seed bank numbers. And, if in doubt, contact your local CCE specialist for help with identification or other management practices.