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CONSERVATION FARMING
UPDATE - December 1995 "Green Bridge" Alert!! -- Plan Fall or Early Spring Control!Roger Veseth, WSU/UI Conservation Tillage Specialist Don't let the "green bridge" cut your spring crop yield potential. Abundant fall rains and mild temperatures across the Inland Northwest have resulted in extensive populations and growth of volunteer grain and weeds this fall. Under minimum tillage or direct seeding of spring crops, the volunteer grain and weeds growing between crop harvest and spring seeding can serve as a "green bridge" host for root diseases and other pests. Growers should control this green bridge in late fall or early spring while maintaining surface crop residue to optimize water conservation -- in order to achieve the high spring crop yields now possible in much of the region.
Northwest
research has shown that spraying volunteer and weeds with a nonselective
herbicide in late fall, or at least about 3 weeks before spring seeding,
can increase yields of direct-seeded spring cereals after cereals by 20
to 50 percent compared to spraying 1 to 3 days before seeding. The 1-
to 3-day time interval that has commonly been used between spraying and
direct seeding can greatly increase the level of root diseases such as
Rhizoctonia root rot, Pythium root rot and take-all. Spring pulse crops
can also be impacted by the green bridge.
When
weather conditions permit, fall spraying when plants are still actively
growing can provide the longest possible "host-free" period for reducing
spring crop pests associated with the green bridge. Nonselective herbicides
can be very effective in late fall because added winter stress helps kill
the plants. In addition to minimizing root diseases, fall green bridge
control can improve control of winter annual weeds, reduce populations
of Hessian fly, Russian wheat aphids, and aphids carrying barley yellow
dwarf virus, and reduce the carryover of disease inoculum for Cephalosporium
stripe of winter wheat.
Why
not till? Intensive tillage generally provides effective control of root
diseases and other crop pests associated with the green bridge, although
some yield losses have been documented when the green bridge was tilled
out shortly before spring seeding. The major disadvantage with more intensive
tillage is greater evaporation and runoff losses which reduce soil water
storage and associated crop yield potential.
On-farm
testing is an easy and effective way for growers to determine the yield
benefits of early green bridge control with their tillage system, crop
rotation and volunteer/weed situation. If growers plan to spray the whole
field, they can turn half the sprayer boom off and on in the field to
make four side-by-side comparisons. An alternative approach could be to
only spray four strips in the field, each with an adjacent no-spray strip
for yield comparison. Each strip should be wider than the combine header
and as long as possible, preferably 500-700 feet or more, for accurate
yield comparisons.
Growers interested in setting up a green bridge on-farm test are encouraged to contact their county extension agent or Roger Veseth, WSU/UI Conservation Tillage Specialist (208-885-6386) for assistance in establishing and evaluating the trials. Ask for a copy of "Green Bridge Key to Root Disease Control," PNW Conservation Tillage Handbook Series No. 16 in Chapter 4, that summarizes 5 years of field research on green bridge management in the Northwest. A 15-minute video (#VT0040) on the topic is also available through WSU Cooperative Extension. |
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 Contact
us: Hans Kok, (208)885-5971
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