Weeds to Be on the Lookout For (August 17, 2016)
Despite the development of new herbicides and other control techniques, weeds are
as much of a problem today as they have ever been. Those that can be controlled
diminish over time while those that are difficult to control become more widespread.
New weed species are constantly being introduced. Some of these become established
and others never do for a variety of reasons including cropping patterns, climatic
conditions, registered herbicides , management practices and other conditions. There
are a few species that have become established in other regions around Yuma but
have never become widespread here. Some that you should be on the lookout for are:
Common Groundsel (Senecio vulgaris)
This is a winter annual that is has been established in the surrounding states for
many years. It first started to appear in La Paz County,Az. about 15 years ago and
is now widespread there and in the Imperial valley. It is mostly in alfalfa but
also present in many other crops. It is in the composite or sunflower family but
is more difficult to control than most other weeds in this family. Oxyfluorfen will
control small groundsel in cole crops but it is difficult to control selectively
pre or postemergence in lettuce. It is best if you can germinate and kill it prior
Hairy Fleabane (Conyza bonariences)
This is classified as a summer annual but it can be found year round in the low
desert. It is often confused with horseweed or marestail (Conyza canadensis).
It has appeared in La Paz county in the Parker Valley, but has not known to be established
in Yuma County. This weed is more gray green and hairy than the horseweed that has
been in Yuma for many years. Fleabane characteristically branches from the base
more than horseweed. Both can be difficult to control. Glyphosate resistant fleabane
is becoming more widespread across the country. The horseweed that has been in Yuma
for a long time still appears to be controllable with glyphosate.
Hood Canarygrass (Phalaris paradoxa)
This is similar to the littleseed canarygrass (Phalaris minor), that has been here
for many years. The seedlings are different and it can be misidentified when it
first emerges. The leaves are broader than littleseed and do not bleed when broken
at the stem. Hood canarygrass was first identified last year in the south Gila Valley.
We had not recognized it previously in Yuma County. The seed head looks similar
but is different. The spikelets have a characteristic hook on them compared to littleseed
which is smooth. Hood Canarygrass is difficult to control postemergence with clethodim (Select)
or sethoxydim (Poast). Neither of these was effective last season.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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