Crop Rotations on Organic Farms

otations, to keep pests in check. They musthave a good working knowledge of insect,disease, and weed life cycles, along withcultural controls that affect pestpopulations. A farmer must also know apest’s feeding habits and preferences, aswell as plant crops that are unappetizing topests prevalent in the region.Needless to say, rotations will not controlall insect pests. <strong>Rotations</strong> have little impacton highly mobile insects because theseinsects have the ability to invade fromadjacent fields or other areas. A good rule ofthumb is to sequence crops in a rotationthat are hosts to entirely different sets ofpests, have different growth habits, and aredissimilar in other respects.All of this helps to interfere with thenormal needs of a pest during its life cycle,such as an insect’s need to find food, apathogen’s need for a suitable host toinfect, or, in the case of weeds, the need fora crop architecture or tillage regime toexploit.In a California study conducted in 1988,researchers M.L. Flint and P.A. Robertsfound that crop pests that can be controlledby rotations had some commoncharacteristics:• The host range of the pest needs to befairly narrow or at least must notinclude plants that are reasonablycommon in a given area.• The pest source should be the fielditself.• The pest must be incapable of survivinglong periods without a living host. Thatis, pest populations must decreasesubstantially within a year or two ofremoving a living host plant. The pestshould be as immobile as possible, suchas soil and root-dwelling nematodesand soilborne pathogens (if they do notproduce airborne spores, such asRalstonia solanacearum).Carefully Plot Your Tactics in the War onInsect PestsInsect pests that are less mobile and that feedon specific plants in limited areas are theeasiest to control. Employing rotations in thebug battle boils down to making it as hard aspossible for insects to find the host plants theylove.Farmers try to disrupt insect growth andbreeding schedules by including nonsusceptiblecrops in the rotation. Whenfarmers expect problems from particularinsects, they may want to physically separatesusceptible species with non-susceptiblespecies and thus make it harder for insects tocross over to crops they favor.Another tactic is to include cash or covercrops in the rotation that will attract thebeneficial insects that help keep pestpopulations in check. Researchers in Georgiareported high densities of big-eyed bugs,ladybugs, and other beneficial insects invetches and clovers planted as cover crops(Bugg and Waddington, 1994). There isanecdotal evidence that beneficial insectshave destroyed Colorado potato beetlesfeeding on eggplant planted into strip-tilledcrimson clover.Organic Production—<strong>Crop</strong> <strong>Rotations</strong> on Organic Farms 13