Late Leaf Rust of Brambles in Home Fruit Plantings

Late leaf rust can be a problem on fall-bearing raspberries.
Late Leaf Rust of Brambles in Home Fruit Plantings - Articles

Updated: August 8, 2017

Late Leaf Rust of Brambles in Home Fruit Plantings

The disease infects red and purple raspberries but not black raspberries or blackberries. This rust, unlike orange rust, is not systemic.

Symptoms

Yellow masses of spores are noticed primarily on fall fruit of primocane-bearing varieties, making the fruit unmarketable. Because symptoms on the fruit do not usually develop until late in the season, infections in plantings of summer-bearing varieties may go unnoticed. Powdery yellow spores also form on the undersides of leaves, causing badly infected leaves to drop prematurely, but this symptom is generally not noticed until infected fruit is seen.

Disease Cycle

There are several species of late leaf rust fungi worldwide. In our region, Pucciniastrum americanum is believed to be the causal agent. White spruce and Engelmann spruce serve as alternate hosts, and their closeness to a planting may increase the likelihood of occurrence. Spores are produced on infected spruce needles in early summer and can infect raspberries. High humidity is necessary for infection to take place. The raspberries will show symptoms shortly afterward. However, spruce are thought not to be necessary for the rust to survive in a planting once infected since this disease has occurred in successive years in plantings with no spruce in the vicinity. Spores are disseminated by wind but may also be physically moved from infected to uninfected plantings by people or machinery.

Disease Management

Clean nursery stock is important since planting stock can be the initial source of inoculum. Control is aided by cultural practices that increase air circulation within the planting such as thinning canes, keeping rows narrow, and practicing good weed control. Prune fall bearers to the ground; do not keep canes around for a summer crop and rake and dispose of all old leaves. Removing floricanes and infected primocanes in winter will reduce the amount of inoculum. This disease has been especially problematic on summer-bearing Festival and fall-bearing Heritage and Jaclyn. Fall-bearing Josephine and spring-bearing Nova and Esta red raspberries tend to be resistant. Because this fungus is not systemic, eliminating the disease from plants is possible. Refer to Table 7.5 for pesticide recommendations.

The important insects and diseases to be controlled, except for viruses, are listed in the right-hand column of this spray schedule. Always consult the label before making pesticide applications. Labels vary greatly among commercial products of the same material. It is important to refer to the label for the best timing and application rates when applying pesticides. Also read the text for information on cultural practices to minimize the application of pesticides. Due to a wide array of various products containing the same active ingredient, for insecticide recommendations, when appropriate, the active ingredient is listed instead of the name of the formulated product.

Table 7.5. Pesticide recommendations for brambles. (Follow all instructions and application rates listed on pesticide labels.
Time to Spray
Suggested Materials
Pests to be Controlled
Dormant (blackberries) - before buds open
Lime sulfur
Anthracnose, cane blight, powdery mildew, rust
Delayed Dormant - just as buds begin to open
Lime sulfurAnthracnose; spur blight on raspberries; powdery mildew, rust, and cane blight on blackberries
New shoots 8 inches long
Sulfur; Malathion; Esvenvalerate
Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; plant bugs
Petal Fall
Sulfur; Carbaryl plus Rotenone or Pyrethrum
Anthracnose; Botrytis, cane blight, and spur blight on raspberries; fruit worms; rose chafer; aphids; mites; plant bugs
PreharvestSulfurFruit rots
MidharvestSulfurFruit rots
PostharvestMalathion plus Carbaryl
Aphids, if present; Japanese beetles

Instructors

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