The so-called “green bridge” could be stealing yields from no-till fields without the growers’ knowledge. The green bridge is the method by which soil and foliar pathogens feed on cover crops, weeds or volunteer crops and survive long enough to infect a new season’s cash crops.

In the soil, the pathogens feed on the roots of the cover crops, weeds or volunteer crops, then move to the roots of new crops. In cases of foliar diseases spread via the green bridge, the pathogens travel on mites from the green or dying cover crops, weeds or volunteer crops to the emerging crops. In both cases, the pathogens quickly attack the young, vulnerable plants and begin reducing yield potential even before the crop is well established.

A Growing Understanding

Though not widely known, the green bridge has been recognized and studied for more than a decade in the Pacific Northwest, where weather conditions sometimes favor its appearance. Green bridges are believed to be behind the region’s loss of spring crops in no-till fields to root diseases during the 1970s and ’80s, and the problem can also occur with fall-planted crops.

It is thought that green bridges could also pose threats in other regions, and no-tillers from Missouri reported during the 2004 National No-Tillage Conference that the problem might be arising in their fields. It is not known how winter conditions might influence the survival of the pathogens and their transition from one crop to another.

According to Diana Roberts, an agronomist with…