How to Manage Pests

UC Pest Management Guidelines

INTEGRATED WEED MANAGEMENT

Weeds reduce kiwifruit vine growth and yields by competing for water, nutrients, and space. They also interfere with low-volume irrigation emitters, reducing the uniformity of water output and efficiency of the system. Weeds must be controlled in kiwifruit orchards, especially in the area around the base of the vine, for optimum yields and health of the vines. Generally the more area that remains weed free, the greater the vine growth. The first 4 years of a vineyard's life are most critical; by about the fourth year the effect of competition is somewhat lessened as vines become established and shade from the canopy reduces weed growth.

In kiwifruit vineyards, weeds are commonly controlled either mechanically or chemically in a 4- to 6-foot-wide strip down the vine row and the area between the vines is either mowed, tilled or in a few instances, chemically treated. During the first four years in a vineyard, weeds in the alleys may need to be mowed or tilled as many as 8 to 10 times per growing season to reduce weed competition. As vines become established and shade weeds, the number of mowings or cultivations will decrease.

A well-managed cover crop between the rows will reduce weed growth. To keep competition to a minimum, the planted cover should be a winter annual. If there is danger of frost in spring, however, be sure to mow it.

Frequently two or more herbicides must be combined to achieve adequate weed control. The weed species present will determine which herbicide combinations are needed. This may include more than one preeemergent herbicide or, more frequently, a combination of a preeemergent and postemergent material.

Herbicides. There are very few herbicides registered for use in kiwifruit vineyards. However, combinations and/or sequential applications of the available herbicides can provide effective and economical control. Before using any herbicide, always read the label, determine what weed species need to be controlled, and follow the directions carefully.

Most commonly, herbicides are used just in the vine row to control weeds. This reduces the total use of herbicides and also keeps the surface roots in the vine row from being cut by equipment. Preemergent herbicides are used to control weeds before they emerge. They can either be applied in fall after harvest or the treatment can be split into two applications: fall and spring. Most preemergent herbicides must be incorporated with water, so unless the orchard has solid set sprinklers, the application must be followed shortly by adequate rainfall. Postemergent herbicides control weeds already growing in the vineyard and should be applied whenever monitoring indicates a need. They may be combined with a fall or spring preemergent treatment or applied as spot treatments during the growing season.

Frequently two or more herbicides must be combined to achieve adequate weed control. The weed species present will determine which herbicide combinations are needed. This may include more than one preemergent herbicide or, more frequently, a combination of preemergent and postemergent material.

MONITORING

Many different summer and winter annual and perennial weeds are found infesting kiwifruit vineyards in California. To make the best choice of control practices, conduct weed surveys at least twice a year: winter and spring. In January or February, determine which species of winter weeds are present. By May or June, summer annuals and perennials will be present. These surveys can lead to better decisions on herbicide choice or cultivation equipment and practices. To prevent weed shifts or herbicide resistance from occurring, monitor treated areas and remove escaped weeds chemically, mechanically, or by hand. Keep written records of monitoring results. Use Grower's Weed Identification Handbook, UC/ANR Publication 4030, to help identify weeds. Check the susceptibility charts to determine the best herbicide(s) to use for optimum control.

WEED MANAGEMENT BEFORE PLANTING

There are a number of ways that weeds growing at the base of the vines can be controlled, including mulching, various forms of cultivation, and herbicides.

Synthetic mulches of polyethylene, polypropylene, or polyester can be used around young vines; polyethylene mulches, however, do not allow air and water into the soil. Young vines may also be hand-hoed until they are 3 to 4 years old, when a swing mower can be used to control weeds. Other mechanical tools available include disks, weed knives, cultivators and rotary tillers. Avoid hitting the trunk of the vine with cultivators. Also, cultivate shallowly next to the vines to keep roots from being injured.

An especially effective method of control before planting vines is to cultivate, irrigate to germinate new weeds, then cultivate again. This reduces the weed seed population in the soil, thus reducing weed growth. At least two cycles of cultivating, irrigating, and cultivating again should be used to make marked reductions in weed seedlings. This method will effectively control annuals, but is not effective on perennial weeds if irrigation is used to keep soil moist.

To control perennial weeds such as dallisgrass, bermudagrass, and johnsongrass, cultivate the soil when it is dry to cut the rhizomes into small pieces. Rework the soil to pull new rhizomes to the surface and dry them out as well. If the soil is irrigated or rain occurs before total control of the perennial plant is achieved, this practice will be only partially effective. If the soil is worked when wet, it will increase the population of these weeds. Even if all of the perennial parts of the weeds (i.e., rhizomes, stolons, etc.) are controlled, the seedlings of the plants must also be controlled when irrigation or rainfall occurs; otherwise these perennials will reestablish.

Herbicides. Because preemergent herbicides have some residual life in the soil, they must be used well ahead of planting or not used until after the vines have been planted and irrigated. It is safer to young vines to control perennials before planting. Established perennial grass weeds can be controlled with glyphosate followed in 2 to 3 weeks with cultivation. If the soil and plant material can be dried after treatment by withholding irrigation in summer, increased control is achieved. This is not feasible in winter. Field bindweed will be partially controlled with this method. Yellow nutsedge plants will be controlled, but new plants will emerge from nutlets underground. In most cases, repeated treatments of perennial weeds may be required.

Another method that can be used for control of most annual and perennial weeds and control of many other soilborne pests is to preplant treat with a fumigate such as metam sodium (Vapam). Follow directions carefully in relation to soil moisture and timing and method of application to achieve the best results.

WEED MANAGEMENT AFTER PLANTING

After planting,weeds can be controlled both culturally and chemically. Hoeing or using weed knives in the row and cultivating between the rows are cultural methods that must be performed frequently to keep weeds from seeding and to reduce competition. If weeds are allowed to mature, not only do the plants often become a fire hazard, but more importantly, they produce enough seeds for many years of weeds. Black polypropylene mulches are also available. These mulches allow water to percolate through into the soil and they can prevent weed growth. They work well in vineyards irrigated with low-volume emitters (drip and microsprinklers), but they are quite costly. To reduce costs, mulches can be limited to a 2 x 2 foot or 3 x 3 foot area under the emitters.

Herbicides. Herbicides are commonly used in strips down the vineyard row. By removing weedy plants from around the base of the vine, not only is weed competition reduced, but the potential for rodent damage as well.

The safest herbicides to use around a vine are those that are used preemergence to the weeds. Postemergent herbicides may be used either alone or combined with a preemergent herbicide to give kill of the existing weeds plus residual control of seedlings. Postemergent herbicides are also used to spot treat perennial weeds during the growing season.

PUBLICATION

UC IPM Pest Management Guidelines: Kiwifruit
UC ANR Publication 3449
Weeds
K. J. Hembree, UC Cooperative Extension, Fresno County
Acknowledgment for contributions to the weed section:
C. L. Elmore, Vegetable Crops Weed Science, UC Davis

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