Take advantage of fall weed management in blueberries

Fall can be an important time to control weeds. Here are a few tasks that should pay off in the future.

Scout your fields

Spend some time after harvest walking fields and recording weed pressure and determine how successful your spring preemergent herbicides were. Note where control was good and poor and which weeds are present, particularly where perennial weeds have become established. Birds drop seeds of many noxious perennials (Virginia creeper vine, grapevine, poison ivy) in blueberry fields, so even clean fields need to be monitored for new weeds. Is weed pressure related to the soil type or herbicides used last spring?

This information will help in formulating a weed management program for next spring. Are rows completely devoid of weeds in the fall? This might indicate too much herbicide was used the previous spring. Some annual weeds should begin establishing in the fall if rates are optimum.

Treat tough perennial weeds

Late summer and fall is a good time to work on tough-to-control perennial weeds such as Virginia creeper vine, grapevine, milkweed, goldenrod, poison ivy and brambles. These perennials generally do not respond to soil applied herbicides, but can be managed by careful applications of glyphosate (Roundup) late in the summer. Glyphosate is effective on these weeds, but can also kill blueberries. Perennial weeds are killed because the chemical moves to below-ground plant parts. Treat before weed leaves senesce. Virginia creeper vine, for example, drops leaves early in the fall. For spot spraying perennials.

  • Use 2 percent glyphosate solutions.
  • Add ammonium sulfate to improve absorption.
  • Avoid all green blueberry tissues.
  • Apply when weeds are still green.
  • Spray at low pressure to limit drift.

Use extreme care not to contact green blueberry tissues (stems and leaves) with glyphosate. Glyphosate absorbed by blueberry leaves and green bark moves within the bush and can kill whole canes or bushes. Weeds such as blackberry, Virginia creeper and grapevine may need to be pulled out of bushes so they can be treated safely. This may seem too slow to be practical, but consider what these weeds cost in lost income. Bushes covered by Virginia creeper vine may yield just 20 percent of their potential. This easily equates to a $5 to $10 loss per bush. The loss is incurred each year and increases as the vines spread to neighboring bushes. Investing 15 minutes to carefully pull vines out of that bush and safely treat them on the ground is money well spent.

Virginia creeper, grapevine and poison ivy can be tough to control
Some perennial vines that warrant extra time to control include grapevine (top left),
Virginia creeper (right) and poison ivy (bottom left).

Fall application of preemergent herbicides

October and November is often an effective time to apply preemergent herbicides. Fall is less busy than spring for most growers and often we have periods of good conditions in the fall. In recent years, rainy periods in the spring have hampered herbicide applications and sometimes delayed applications until after weeds have established, so control is poor. Over the last three years, we have compared spring and fall applications of several standard herbicides. Most provided comparable control in both seasons. Fall may be better than the spring for control of some weeds. Marestail, for example, can emerge in the fall, so spring applications are too late for control.

Consider experimenting with fall applications. Chateau and Solicam are good candidates for the fall, particularly in combination with older materials such as Karmex or Princep. Results of a trial this year (Table 1) showed that fall applications of Solicam plus Princep or Chateau alone provided good weed control through early August. The primary weeds present in this study were red sorrel, common crabgrass, common chickweed, Pennsylvania smartweed and horsenettle. Other trials indicate that fall applications of Karmex, Princep and Solicam are as effective as spring applications.

Table 1. Effect of herbicides applied in fall 2010 and spring 2011 on weed cover in summer 2011. 'Duke' field, South Haven.

Rate lb ai/acre Date Weed cover (%)
15 June 1 Aug

98 100
Princep 90Sinbar 80W 21 Nov 11 52 100
Princep 90Solicam 80DF 22 Nov 11 3 27
Chateau 51% 0.38 Nov 11 6 16
Princep 90Sinbar 80W 21 April 1 87 100
Princep 90Solicam 80DF 22 April 1 83 90
Chateau 51% 0.38 April 1 2 13
Callisto 4SC 0.188 May 10 42 90
Callisto 4SCSinbar 80W 0.0941 May 10 2 10
Callisto 4SCSolicam 80W 0.0942 May 10 6 33
Sandea 75WDG 0.047 May 10 37 98
Sandea 75WDGSinbar 80W 0.0471 May 10 1 17

Dr. Hanson’s work is funded in part by MSU’s AgBioResearch.

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