Orchard Management (1+1)

HERBICIDE CONSIDERATIONS

Herbicide Considerations:

• As discussed in chapter 3 it is advisable to read the manufacturer’s instructions prior to application of any herbicide (Plate 3.3).
• Herbicides sprays are to be directed along each side of the tree row.
• While applying herbicide, ensure that tree trunk does not come in contact with spray material (Plate 3.4).
• Use special nozzles for herbicides application. Use of flat fan nozzles minimize spray drift and allow low-pressure spraying (Plate 3.5).
• It is advisable to apply white latex paint or lime to the bottom 2 to 3 feet of the tree trunk of newly planted trees before applying herbicides (Plate 6.4). Painting the tree trunks reduced the potential for winter as well as herbicide injury, especially from post emergence herbicides.
• As discussed in previous lecture (lecture 3), herbicides are available as pre-emergence as well as post-emergence weed control.

Pre-emergence herbicides:

• Pre-emergence herbicides are applied on the soil soon after tillage operation in spring, while post-emergence herbicides are applied two or three months later on the emerged weeds.
• Pre-emergence herbicides control germinating weeds seeds but usually do not give acceptable control of emerged weeds.
• Rain fall is needed to properly activate most herbicides; however, best control occurs when water (rain or irrigation) is added within a few days of application.
• The desired amount of time for rainfall after application varies by herbicides.

Post-emergence herbicides:

• Post emergence herbicides control emerged weeds and is most effective when applied to actively growing weeds.
• Weeds under stress from drought or mowing may not be adequately controlled by post emergence herbicides.
• If weeds are stressed from drought, delay herbicide application until after adequate rain fall when weeds are no longer wilted.
• If weeds have been mowed, wait several days to allow re growth before applying herbicides.
• Symptoms of herbicide activity may not be noticeable for up to two weeks after application of Glyphosate, Sethoxydim, clethodim, or fluazifop (Roundup, Poast, Select, or Fusillade DX, respectively).
• Effects of Glufosinate, Paraquat, and 2, 4-D are noticeable in 1 to 3 days after application.
• Some post emergence herbicides require the addition of a surfactant or crop oil to improve herbicide activity.
• Remember, surfactants and crop oil differ from another and may not be interchangeable.

Time of application of herbicides

• Major objectives of weed management is to reduce weed competition with the fruit crops particularly during the first 6 to 8 weeks after bud swell and keep the area under the trees weed-free through harvest. Timing of pre emergence herbicide application is important in accomplishing this goal.
• As has been discussed above, generally single application of pre-emergence herbicide is given in spring followed by post emergence herbicide application later.
• However, it can be difficult to spray underneath limbs loaded with fruit in mid and late summer.
• With appropriate pre emergence herbicide timing, post herbicide application in mid and late summer can be avoided. Several timing options have been listed below.

Fall/ Spring Split.

• One approach is to apply a nonselective burn down herbicide (Glyphosate or Paraquat) in the fall after early harvest (November).
• The fall application will generally provide pre emergence control into the early summer.
• When fall pre emergence treatment breaks and emerging weeds get 5 to 8 cm tall, another pre emergence herbicide application with a burn down herbicide should be applied.
• Fall herbicide application may be helpful in managing voles. In areas where erosion is a concern, this option may not be acceptable.

Weed scouting: It is important to scout orchards regularly to determine weeds if present. Scouting allows growers to:

• Recognize the need to control escaped weeds with a timely herbicide application and
• For early identification of difficult-to control weeds. Early identification of problem weeds can prevent them from becoming established in the orchard.
• If problem weeds are noticed for the first time in an orchard, they need to be removed before they produce seed. This can be done by hands or with a spot treatment with a nonselective post emergence herbicide like Glyphosate, paraquat.
• Scouting also gives growers an opportunity to recognize poorly controlled weeds so their weed management program can be adjusted.
• Another aspect growers should consider is the potential for infestation of weeds from around the border of the orchard. Weeds in these areas produce seeds that will find their way into the orchard.

Chemical Mowing

• Some herbicides can be used at sub-lethal doses to suppress orchard floor vegetation.
• Timing and rate will vary with the vegetation present.
• Generally, tall fescue can be used as the guiding species, because it is a major component in most orchards.
• Optimum timing for suppression is when tall fescue has 5 to 10 cm of new growth in the spring.
• Glyphosate can be recommended for this operation.
• Chemical suppression of grasses should be done only to healthy, well-established sod.