GREEN AND GROWING D. Bruce Bosley Extension Agent/Cropping Systems Colorado State University Extension 508 S 10th Ave., Ste 1, Sterling Co 80751 (970) 522-3200 Ext. 285 Bruce.Bosley@colostate.edu FOR IMMEDIATE RELEASE – June 28th, 2011 Crop Rotation Rotating crops has been seen as a valuable cultural practice proven to reduce plant diseases and pest problems as well as improving soil health and plant productivity. Agricultural references to crop rotation have been found in literature from ancient Rome and civilizations in Southeast Asia prior to 100 B.C. Northeast Colorado dryland producers have incorporated rotations in their cropping system to make more efficient use of the rain and snowfall that we receive each year. Most of our irrigated crops yield better and have fewer insect and disease problems when grown in a rotation. It can be claimed that continuous irrigated corn is the one exception in Colorado. We can attribute this in large part to our dry climate, advances in crop genetics, and improvements in crop production and pest management practices. However, today I’ll focus on those crops where rotation is beneficial especially in reducing crop diseases. Irrigated and dryland wheat producers have often noted that while they can grow wheat back to back in subsequent years the second crop never has the same yield potential as the first crop even when rainfall and climate are favorable for winter wheat. Many farmers have also discovered that their wheat crops yield better following corn and grain sorghum as well as other crops in a multiple year rotation. Consequently, we see dryland producers raising three and four year wheat based crop rotations that are both more profitable and better at protecting from soil erosion than the traditional wheat fallow rotation. Many plant non-grass crops such as sunflowers and experimenting with canola and peas to optimize the benefits of crop rotations. Continuous cropping wheat and traditional wheat-fallow rotations often encourage soil borne diseases. I have found damaging levels of Fusarium (dryland) foot rot on irrigated and dryland fields in Northeast Colorado. It is best to rotate crops to reduce Fusarium foot rot inoculum and avoid planting wheat following corn or wheat. Take-all is a significant risk in irrigated wheat when growers plant it two or especially more years in a row. Crop rotation is the most practical, economical and successful means of control of take-all. Rotations with soybeans, other legumes, or corn is most satisfactory. A rotation with two years between wheat crops is highly recommended. Alfalfa suffers from many soil and crown diseases in later years of its production in fields. Crown rot is chief cause for yield decline in alfalfa. Crown rot comes from a complex of common soil organisms including Fusarium, Pythium, and Rhizoctonia. Crown rot arises naturally with the age of the stand but is often increased by mechanical weed control efforts when harrows or disks are used. Stem nematode is another alfalfa disease that can occur in irrigated fields. Rotation with non-host crops such as sorghum, small grains, beans, and corn on a 2- to 4-year basis should reduce alfalfa stem nematode populations. Use longer rotations where stem nematode has become a problem in a field. Selection of nematode resistant alfalfa varieties can help in reducing this disease. Use clean, nematode-free seed. Avoid moving contaminated farm machinery or livestock from an infested field to a clean field. Avoid using contaminated wastewater or tail water. Keep manure from feedlots where cattle have been fed infected hay out of clean fields. Also, cutting alfalfa fields only when the top 2 to 3 inches of soil are dry should help reduce re-infestation. University trials demonstrate that frugal applications of irrigation water to keep soil surfaces dry will minimize spread into later cuttings. Please contact Bruce Bosley for questions on these and other cropping systems topics at (970)768-6449 or firstname.lastname@example.org. Extension programs are available to all without discrimination. If you have a disability for which you seek an accommodation, please notify Bruce Bosley 7 days before the event. Colorado State University Extension, U.S. Department of Agriculture and Colorado Counties Cooperating.