MSU Extension IPM Bulletin, Fall 2014

Fall 2014 Crop harvesting and weed management by Fabian Menalled, MSU Crop Weeds Specialist, Department of Land Resources and Environmental Sciences Many times we think of crop harvesting and have resulted in an increased weed survivorship weed management as two independent tasks. and growth? Carefully considering these and Yet harvesting provides a great opportunity other potential mechanisms responsible for the to improve weed management. First and success of the weed population you detect in a foremost, while in the combine farmers have particular feld can help adjust the management a unique opportunity to refect on the season’s approach to prevent the growth of these patches. successes and failures. Systematically travelling Post-harvest weed management. Weed across the felds provides a great chance to species such as kochia are diÿcult to control refect on approaches for the next crop’s weed once they have been cut by the combine management program by carefully checking because they drop their seeds in one spot. locations of which species thrived this year. ˛e Because kochia seedlings can emerge at any next step is to fnd out what went wrong and time during the winter, they can produce what can be improved. ˛e following is a list of dense clumps of seedlings which are very hard some of the many things farmers could think to control as their mass impedes e˙ective about at harvest. herbicide coverage. Post-harvest treatments Weeds occur in patches. In general, weeds with glyphosate (Roundup and other generic are not distributed uniformly across felds but names) and paraquat applied late August FIGURE 1. Wheat field. Photo courtesy of to early September when kochia plants are USDA-ARS. in patches of high densities. Several causes could be responsible for these patches. Is actively growing and have produced enough it possible that you have selected herbicide leaf tissue for herbicide absorption can help to INSIDE: resistant weed biotypes? Did you get bad crop substantially reduce seed production. However, Crop harvesting and weed establishment during the summer that resulted post-harvest herbicide options should not be management ...................................1 in a less competitive canopy at the site of the based or planned solely on the weed species weed patch? Is there any underlying nutrient currently in the feld, but also take into account Sugarbeet Intergrated Pest the spring planting intentions. Management Impacts .....................2 or moisture characteristic at that site that could Regional Private Applicator Programs ......................................3 What’s that grass growing on the other side of the fence? ............................4 Wheat Head Armyworm ................5 Ask the Expert ................................6 Pest Management Tool Kit .............7 Meet Your Specialist .......................8 FIGURE 2. Barley harvest. Photo courtesy of USDA-ARS. (Crop Harvesting, continues on page 2) 2 (Crop harvesting, continued from page 1) Impact of harvesting on weed and fower and complete their life cycle the Cooler temperatures trigger the movement communities. Weed species are di˙erently following summer. Farmers increasing acreage of food reserves down to the root systems, infuenced by crop harvesting operations and of winter crops shouldn’t be surprised that enhancing movement of herbicides to the their strength and selectivity depend on timing winter annual weeds become a widespread plant’s root system and improving control. and technique. For example, repeated growing management issue. Managing winter annual However, farmers should be aware that of the same crop harvested at similar times weeds starts in fall when they are more perennial species vary in sensitivity to frost, and by similar methods selects specifc weed susceptible to weed control practices and and the application window di˙ers between species. ˛e timing of harvest and stubble scouting for their presence can give a head species. For example, Canada thistle can height are decisive selective factors for which start on management. survive light frosts and is e˙ectively controlled weed species will produce seeds, the amount Harvest the weediest feld last and with relatively late fall herbicide applications. of seeds being produced, as well as dispersal carefully clean the combine. Leaving the Other perennial weeds such as hemp dogbane patterns. For example, high stubble can lead worst felds for last is a simple approach to and common milkweed complete their life to higher seed production of species such as minimize the spread of weed seed and has cycles by late summer and do not tolerate frost common mallow or prostrated knotweed. been shown to be economically e˙ective. well, so fall herbicide applications should not Variations in timing and methods of Carefully cleaning equipment is another be delayed when controlling these species. harvesting and diversifed crop sequences can simple approach to minimize the transfer Finally, although fall application will not help avoid selecting for specifc and diÿcult to of weed seeds between felds. ˛ese simple guarantee excellent control of feld bindweed, manage weed species. steps can help farmers minimize the spread of late control practices can be e˙ective, provided Managing winter annual species. Winter weeds, including herbicide resistant biotypes. there is re-growth of this species. ˛ese are just a few fall season annual species such as cheatgrass and Fall is the time to manage perennial weeds. considerations farmers can take into account jointed goatgrass germinate and emerge in As fall temperatures cool, growers have an to develop e˙ective integrated weed control late summer, become semi-dormant and opportunity to manage perennial weeds. overwinter, resume growth in early spring, programs. Sugarbeet Integrated Pest Management Impacts in Montana by Barry Jacobsen, Interim Department Head of Montana Agricultural Experiment Stations and Agricultural Research Centers, MSU Professor of Plant Pathology Cercospora leaf spot reduced sugar production with strong resistance management training of tonnage per acre by 10-12% and dramatically both growers and feld workers. To date sugar increased storage losses. In 1996 there was beets have not lost another class of fungicides widespread resistance to the key benzimazole to resistant Cercospora isolates, while fungicides, which were commonly used to resistance to the QoI fungicides in Minnesota, treat Cercospora leaf spot, and great concern North Dakota and Michigan have resulted in about resistance to other fungicide alternatives. this class of fungicides being lost to growers in Something needed to be done. those states. Infection and sporulation by the Historically sugarbeet varieties with Cercospora leaf spot pathogen is strongly resistance to Cercospora have also had very a˙ected by environmental conditions, low yield potential. We began evaluating and a weather-based prediction system varieties with varying levels of resistance FIGURE 3. Cercospora leaf spot early defoliation. Photo by Barry Jacobsen. borrowed from the Minnesota/North Dakota and demonstrated that varieties with partial production area was adapted for Montana. resistance could be sprayed with fewer Sugarbeets are grown on 60,000-70,000 Sugarbeet company feld workers were trained fungicide applications with no loss in yield acres in Montana, with 35,000+ acres in the use of the system and feld monitoring compared to susceptible varieties sprayed with grown in the Sidney Sugars factory district techniques, and they communicated infection four fungicide applications. Based on this and 30,000 acres in the Western Sugar period information to growers. ˛is resulted research and Extension education programs, Billings factory district. ˛ese two areas have in better and more e˙ective timing for the Sidney Sugars reduced its variety requirements somewhat di˙erent challenges. From 1990- frst fungicide application, and growers saved to a KWS rating of 5.3 or less. ˛is was a 2000 the key problem in the Sidney Sugars on the average $15-16 per acre (about one signifcant change from no prior Cercsopora factory district was Cercospora leaf spot. spray per year). In addition, new classes of resistance requirement or varieties having Growers sprayed each acre four times per fungicides were identifed and labelled along year with fungicides to control this disease. (Sugarbeet, continues on page 4) 3 Regional Private Applicator Programs by Cecil ˜arp, MSU Pesticide Education Specialist, Department of Animal and Range Sciences employees) pesticide applicators. For calibration demonstrations using on-site receiving your commercial or government spray equipment as well as interactive applicator license contact Jolene demonstrations of pesticide exposure Warnke-Roszel, Montana Department and personal protective equipment. of Agriculture, (406)444-5400. For Presentations will also focus on many more information on the private (farm) herbicide fate scenarios that impact applicator license, see the MontGuide Montanans including 1) non-target titled ‘˛e Montana Private Applicator pesticide toxicity in homeowner gardens, 2) Program’ at www.pesticides.montana.edu/ why over 70% of private applicators spray by selecting ‘Reference Materials’ and ‘PAT in high wind, 3) non-target damage from in Montana.’ spraying in high wind and 4) how to avoid FIGURE 4. Pesticide applicator training. Photo by Cecil Tharp. ˛e MSU Pesticide Education Program these growing threats. Individuals applying pesticides on land is

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