Field bindweed control in wheat: Fallow rotations

Field bindweed, often known as 'morning glory' to Pacific Northwest growers, is commonly listed among the world's worst weeds. Field bindweed, (Convolvulus arvensis), is extensively distributed in cultivated fields in the western United States, and can be a persistent problem in dryland wheat. It is a perennial weed with an extensive root system that can penetrate the soil to a depth of 20 feet. Seeds can remain viable for more than 30 years. Field bindweed spreads both vegetatively and by seeds. Numerous lateral roots develop mostly in the top 2 feet of soil. Buds formed on these lateral roots are capable of developing into shoots. Root segments containing buds are spread by tillage implements. Dense stands of field bindweed can reduce cereal yields by 20-50 percent.

Field bindweed has traditionally been suppressed with repeated tillage in fallow. Several currently available herbicides can also suppress bindweed, although a single herbicide application will rarely eliminate established stands. Multiple herbicide applications are usually necessary for suppression. Herbicide performance often varies due to differences in plant and environmental conditions. Bindweed under moisture or heat stress has smaller leaves with more surface wax on the leaves and is, therefore, difficult to control.

In wheat - fallow rotations, treatment of bindweed in fallow after 12 inches of new growth has been made in the late summer is an effective time for control. At this time, bindweed is vigorously growing and herbicides can be used in fallow without concern for injury to wheat. However, phenoxy-type herbicides such as 2,4-D or dicamba (Clarity®, Banvel®) should not be used near horticultural crops, particularly grapes during sensitive periods. Grapevines and many ornamental plants are extremely sensitive to phenoxy-type herbicides. These plants are sensitive to phenoxy herbicides throughout the growing season, but grapevines are most vulnerable from budbreak through the bloom period (early April to late June).

A trial was conducted near Mission, OR in Umatilla County to evaluate sequential herbicide treatments for long-term suppression of field bindweed at times deemed to be less sensitive to grapevines. Treatments were applied in the late summer of the fallow period (September 7, 1999) and again after wheat harvest (September 14, 2000). All fallow treatments provided good control of field bindweed in the following winter wheat crop (June 29, 2000 evaluation). However, a sequential treatment after wheat harvest was necessary to obtain extended bindweed control in stubble the following spring (May 18, 2001 evaluation). Sequential treatments containing Paramount® or Landmaster® provided better extended bindweed suppression than did sequential applications of 2,4-D or Clarity, or a single Paramount application (see table). Sequential Paramount applications did not provide a significantly greater level of bindweed suppression than sequential Landmaster applications.

When planning an aggressive strategy for bindweed management, well timed, sequential herbicide applications are effective. If tillage is used as an additional tool in an integrated management program, it needs to be timed to allow bindweed regrowth prior to herbicide spraying. Applicators also need to also maintain a constant awareness that sensitive crops can be adversely affected by bindweed applications.

• 1Treatments applied in summer fallow September 7, 1999. Wheat seeded September 30, 1999. Sequential treatments applied after wheat harvest on September 14, 2000. Methylated seed oil added to all treatments at 2 pt/A except for Landmaster which received Ammonium Sulfate.