Weed Control Options and Strategies for
Direct Seeded Pulse Crops

 

Joe Yenish, Extension Weed Scientist, Washington State University, Pullman, WA
Donn Thill, Weed Scientist, University of Idaho, Moscow, ID
Dan Ball, Weed Scientist, Oregon State University, Pendleton, OR

There are now better opportunities to include pulse crops into a direct seeded rotation that is completely or partially no-tillage. Recent innovations in pulse crops breeding and planting equipment is making it possible to direct seed pulse crops. Improved Afila varieties of peas with shorter vines and more upright growth than conventional varieties are more conducive to harvest without a pea-bar attachment on the combine or swather. This means that seed beds do not need to be worked as finely nor smoothed with a roller or packer following planting. Thus, greater amounts of residue will be preserved from the previous crop which means less soil erosion. The bottom line is that the soil will be protected better by both the additional residue from the preceding crop and the additional residue from the higher cutting of the Afila peas. Additionally, direct seeding systems can allow pulse crops to be used in more intensive rotations in the medium rainfall areas.

Certainly, weed management in direct seeded pulse crops provides greater challenges than winter wheat or spring grains. For starters there are fewer herbicide tools. However, by using the current tools wisely and integrating new tools into the system as they become available, effective weed management can be achieved.

An important part of direct seed pulse crop production is to select fields wisely. If weed populations are great or the weed species not easily controlled in a pulse crop, then you probably want to select a more competitive crop with greater herbicide options for that field. Remember that pulse crops may be the weakest portion of your existing or potential rotation from a weed management standpoint.

Currently, a common treatment for pulse crops is a preplant incorporated or preemergence application of imazethapyr (Pursuit) in combination with pendimethalin (Prowl) or the prepackage of these chemicals (Pursuit Plus). In no-tillage systems there are limited options to effectively incorporate herbicides and this may reduce weed control efficacy. Early preplant applications of herbicides may preclude the need to incorporate soil applied herbicides to provide more consistent weed control. But how long prior to planting should these applications be made to maximize weed control efficacy and crop yields? The following table shows results from several studies comparing fall and spring preplant applications of imazethapyr in dry peas and lentils. Both dry peas and lentils showed greater yields with spring preplant compared to fall preplant applications. Thus, preplant applications can be effective in no-tillage pulse crop production. Moreover, research has shown that spring preplant applications have a yield advantage over fall preplant herbicide applications.

 

Table. Peas yield in no-tillage as effect by herbicide treatment in no-tillage.

Treatment

Application timing

Rate

Pea seed yield

Lentil seed yields

Lbs. a.i./A

Percentage of weedy check
imazethapyra

fall

preplant

0.047

124%c

179%d
imazethapyra

spring preplante

0.047

133%c

284%d
bentazonb

POST

0.5

115%d

NA
a equivalent to 3 oz. Pursuit/A
b equivalent to 1 pt. Basagran/A
c average of three locations, Endicott, Walla Walla and Pullman, WA
d average of two locations, Walla Walla and Pullman, WA
e spring preplant applied approximately two weeks prior to planting

Postemergence herbicides are commonly mentioned as an important option in direct seeding systems. Postemergence applications of bentazon (Basagran) have resulted in increased dry pea yields under no-tillage (see Table). While it may be possible to effectively control weeds with a total postemergence program, effective postemergence options are limited in pulse crops. Thus, it is best to plan on combining pre- and postemergence herbicides until postemergence weed control systems in direct seeded pulse crops are more developed.

Improved varieties of fall seeded legumes are currently being developed. Research in the Palouse has shown substantial yield potential for fall vs. spring seeded legumes. No-tillage direct seeding of winter legumes is needed to fully realize the greater yield potential. Thus, weed management under no-tillage for fall seeded legumes is needed by default. Research has been started to develop weed management systems for fall seeded peas and lentils.

In summary, weed management in direct seeded pulse crops has been shown to be effective with currently labeled herbicides. As improvements continue to be made in spring and fall seeded pulse crop varieties, improvements will also be needed in weed management systems to fully realize yield and quality potential. Research into better weed management systems is ongoing.


Ds9proJY.wpd