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How to Manage Pests

UC Pest Management Guidelines


Pistachio

Special Weed Problems

(Reviewed 2/07, updated 2/07)

In this Guideline: More about weeds in pistachio:

Many of these special weed problems can be minimized by managing them before planting pistachio orchards.

HAIRY FLEABANE. Hairy fleabane is a summer annual that reproduces from seed, although under certain environmental conditions it can grow like a biennial. It germinates from fall through spring and matures and produces seed from July through September. Hairy fleabane is a member of the sunflower family; its seed is readily disseminated by the wind. Of the preemergent herbicides registered, only isoxaben (Gallery) effectively controls it during the nonbearing period. Hairy fleabane can be difficult to control with a postemergent herbicide because its stems are multi-branched and often woody and it has a lack of significant leaf area. Hairy fleabane plants are most susceptible to control with postemergent herbicides or mechanical control when they are in the seedling stage.

HORSEWEED (MARE'S TAIL). Horseweed is a summer annual weed, closely related to hairy fleabane, with similar growth and reproductive characteristics. Unlike hairy fleabane, horseweed grows as a single stalk. Horseweed can become a prevalent weed where repeated uses of oryzalin (Surflan), napropamide (Devrinol), and oxyfluorfen (Goal) are used preemergence. Control emerged plants when they are in the seedling or rosette stage of growth. Delaying treatments beyond this can result in significant regrowth. Mowing is not recommended because cutting plants off above the soil line can result in the sprouting of lateral buds at the base of this weed.

FIELD BINDWEED. Field bindweed is a vigorous perennial weed that grows from seed, which can survive as long as 30 years in the soil, or more commonly, from reproductive stolons, rhizomes, or extensive roots. It is important to control this weed before it has the chance to produce seed. While cultivation can be used to control seedlings, cultivating mature plants can result in aiding the spread of the reproductive structures. Once field bindweed appears in an orchard, spot treat with high label rates of glyphosate (Roundup, Touchdown) to prevent its establishment.

NUTSEDGE. Yellow and purple nutsedge are perennial weeds that reproduce mainly from underground tubers. Yellow nutsedge is the most common species found in pistachio orchards. Most tubers of yellow nutsedge will survive in the soil for less than 5 years and are found primarily in the top 8" of the soil profile. Yellow nutsedge grows and reproduces best under sandy, well-irrigated conditions. The tuber of each plant has several buds that can each give rise to additional plants. Under normal conditions, one or two buds sprout to form new plants; however, if killed by cultivation or an herbicide, then new buds are activated. Thiazopyr (Visor) is effective at controlling yellow nutsedge before it emerges in nonbearing orchards. Treat emerged plants with glyphosate (Roundup, Touchdown) before they reach the 4- to 5-leaf stage. Repeat applications will be required when new growth occurs.

LITTLE MALLOW (CHEESEWEED). Little mallow is an annual or biennial weed that is sometimes not effectively controlled with preemergent herbicides. High rates of oxyfluorfen (Goal) or thiazopyr (Visor) can provide acceptable control. Once established, little mallow becomes woody and forms a thick crown and root, making it difficult to control mechanically or with postemergent herbicides. Plants that are less than 4-to-6 inches tall are easiest to control with a tank-mix application of oxyfluorfen plus glyphosate (Roundup, Touchdown). Repeated mowing is not an effective means of control.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pistachio
UC ANR Publication 3461
Weeds
K. J. Hembree, UC Cooperative Extension, Fresno County
A. Shrestha, UC IPM Program, Kearney Agricultural Center, Parlier

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