Raspberry Plant Problems: Reasons For Raspberry Canes Turning Brown

Raspberry Plant Problems: Reasons For Raspberry Canes Turning Brown

Isn’t it satisfying to harvest your own raspberries? I love the way a perfectly warm, ripe raspberry rolls off its mount into my fingers. Raspberry aroma is tangy, and the taste of a fresh raspberry is delightfully warm, sweet and tart! Raspberry plants are worth growing. That being said, there are many diseases of raspberry plants so it is good to educate yourself about how to grow the delectable raspberry. Canes turning brown are a common symptom of many different diseases of raspberry plants.

Understanding Raspberry Plant Problems

One of the first things you need to know is the difference between a primocane and a floricane. A primocane is a leafy stalk formed during its first year on a raspberry plant. It may produce buds but doesn’t typically produce fruit. You want to let the primocanes grow and then overwinter for producing flowers and fruit the second year.

During the second year of this cane’s life, it is called a floricane. Floricanes produce flowers and fruit. They typically die or become non-productive after that. You should cut floricanes down to ground level after you harvest your berries. Leaving floricanes uncut can lead to unnecessary raspberry plant problems.

Reasons for Raspberry Canes Turning Brown

Raspberry cane diseases that result in browning can be caused by bacteria or fungi. Browning raspberry canes can also be a sign of normal growth. In general, a floricane is not as lush and green looking as a primocane. It becomes a bit woodier and browner in its second year. This is not a problem.

Bacterial problems

Bacterial diseases include fire blight and bacterial blight. Both of these diseases cause significant browning raspberry canes – very dark or burnt looking stems and leaves are a sure sigh. These diseases can ruin fruit production and are favored by moist, wet springs or winters. They need a wound opening or pruning cut to infect the plant.

It is best to cut out the infected plant material at least 12 inches (30 cm.) below the diseased area. Destroy the plant material. Do not compost it. Copper sprays applied periodically throughout the season can help protect the plant but will not prevent the disease.

Fungal diseases

Some important fungal diseases that lead to raspberry canes turning brown include spur blight, cane blight and anthracnose. Look at your primocanes in late summer or early fall before they harden up for winter to see if you have signs of these diseases.

  • Anthracnose displays round, sunken white to tan colored pits in the internodes of the cane or stem (the areas between leaves or smaller branches). These pits often have a purple margin. The disease weakens and cracks the bark and often leads to death of the cane over the winter.
  • Spur blight initiates its disease course in the leaves or at the node where the leaf attaches to the cane (stem). In the leaves, you’ll see yellowing and browning. The leaves will die and drop off leaving the leaf petiole. On the branch stem, you’ll see little ½ inch (1.3 cm.) purple or brown spots around the nodes. These spots might expand around the entire stem. During the next year, these areas will be non-productive and appear leggy.
  • Cane blight is caused by wounds in the stem. The wounds form reddish-brown streaks and can eventually girdle the entire cane causing cane death.

All three of these fungal diseases of raspberry plants are spread from cane to cane rather than root to cane. They love moist conditions. The diseases may overwinter on the plant and then spread from floricane to primocane. Splashing water spreads transmits the fungi in all three of these diseases. Wind also spreads the fungi of spur blight. The keys to controlling these diseases are:

  1. Reduce moisture and humidity in the area
  2. Keep your rows narrower than 18 inches (46 cm.)
  3. Remove non-productive floricanes every year
  4. Don’t prune if you expect rain in the next 5 days.

In severely infected patches, you can mow the whole area down and start over and/or apply an appropriate fungicide. Note that you may be applying a poison to an edible crop if you use a fungicide. Check the label carefully.

If you are starting from scratch with your raspberry patch, be sure to look for disease resistant varieties. Make sure your patch gets enough sun, regular water and is amended with compost every year.

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Probably the worst and most difficult problem of raspberries as viral infections are incurable. The only solution is to grub up the plants and burn them.Replace with fresh stock and do not plant in the same place.

It is important to buy stock that is known to be free of viruses, as once infected, the canes lose vigour and crops are much reduced. Viruses are transferred from infected plants by aphids, leafhoppers or nematodes.

Symptoms are yellow mottling of leaves or stunted growth. There is no effective control and infected plants should be removed as soon as they are no longer productive. Making sure that weeds do not grow nearby is one way of reducing the possibility of infection, as many of the viruses live in other host plants, many of which are weeds.


MSU Extension

Wilting shoot tips signal that this easy to control pest has found your raspberry patch.

Wilting primocane shoot tip after girdling. Note the two girdles in the background. Photo credit: Mark Longstroth, MSU Extension

This time of year, Michigan State University Extension educators, including myself, get calls from homeowners complaining that the shoot tips of their raspberries are dying. I ask if there are two rings cut into the stem below the wilting. If the answer is yes, I know they have the raspberry cane borer.

Raspberry cane borer, Oberea bimaculata Oliver, is a beetle pest of raspberries that is widespread in Michigan. The beetle lives its life feeding on raspberries. The adults emerge in June. They feed on the tender shoot tips of new raspberry canes. The females lay their eggs about 6 inches below the tips of the new primocanes (first year shoots emerging from the ground). First, she chews two rings around the stem about 0.5 inches apart. Then she lays an egg between the girdles. The girdling causes the stem tip to wilt.

Control is easy and organic, just remove the portion of the stem between the two girdles and throw it in the trash. If not removed, the larvae burrows down the cane to the base and into the crown the next summer. Affected canes are weak and often break or die the next year. The larva pupates in the soil and emerges the next year to attack the shoot tips.

This pest seldom requires insecticide sprays and can be controlled by scouting for wilting shoot tips in the summer and removing the stem sections with the eggs before the larvae can burrow into the cane. If there is a severe pest infestation, pesticide sprays are targeted on the adults in the immediate prebloom period, just before the flowers open.


Left, Close up of raspberry cane borer adult and recently chewed girdles, marking where the egg will be laid. Right, Raspberry cane borer larvae boring into raspberry cane. Photo credits: Mark Longstroth, MSU Extension

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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HARVESTING RASPBERRIES

It's a temptation when harvesting raspberries to pile them high into containers. Don't do this because the raspberries at the bottom of the container will be crushed by the weight of the top raspberries. Try to harvest your raspberries when they are dry, wet raspberries deteriorate quicker than dry ones. Layer them two, at most three, deep in shallow containers, store them in shade whilst harvesting and get them into the fridge as soon as possible. A ripe raspberry will last two, possibly three days in the fridge before it starts to deteriorate significantly.

Frozen raspberries will last three or four months in the average freezer. The freezing process does damage the texture of raspberries so frozen raspberries are ideal for jam, fruit drinks and flavouring. Frozen raspberries can be defrosted in the fridge and used as a topping for morning cereals (our favourite) and also to be added to plain yogurt to give a fruity taste.


Spur Blight of Red Raspberries

Spur blight is caused by the fungus Didymella applanata. Spur blight occurs only on red and purple raspberries. Spur blight has been considered to be a serious disease of red raspberry however, recent studies in Scotland suggest that spur blight actually does little damage to the cane. The extent of damage caused by spur blight in the United States is not clearly understood. The spur blight fungus has been reported to reduce yields in several ways. It can blight the fruit bearing spurs that are produced on the side branches, cause premature leaf drop, and kill buds on the canes that later develop into fruit bearing side branches. In addition, berries produced on diseased canes may be dry, small, and seedy.

Symptoms

Figure 1. Typical symptoms of spur blight on red raspberry canes.

The symptoms first appear on young first-year primocanes in late spring or early summer. Purple to brown areas (lesions) appear just below the leaf or bud, usually on the lower portion of the stem.

These lesions expand, sometimes covering all the area between two leaves. In late summer or early fall, bark in the affected area splits lengthwise and small black specks, which are fungal fruiting bodies (pycnidia) appear in the lesions. They are followed shortly by many slightly larger, black, erupting spots another form of fungal fruiting body (perithecia). Leaflets sometimes become infected and show brown, wedge-shaped diseased areas, with the widest portion of the wedge toward the tip of the leaf. Infected leaflets may fall off, leaving only petioles without leaf blades attached to the cane. When diseased canes become fruiting floricanes during the next season, the side branches growing from diseased buds are often weak and withered.

Causal Organism

Spur blight is caused by the fungus Didymella applanata. It survives the winter in lesions on diseased canes. The following spring and summer, during wet and rainy periods, spores are released and carried by splashing rain and wind to nearby primocanes. There they germinate in the presence of water and produce new infections, where the fungus will again over winter.

Control

Figure 2. Spur blight symptoms on red raspberry leaves.

All steps possible should be taken to improve air circulation within a planting, to allow faster drying of foliage and canes. Reducing the number and duration of wet periods should reduce the potential for infection. Excessive applications of fertilizer (especially nitrogen) should be avoided, since it promotes excessive growth of very susceptible succulent plant tissue. Plants should be maintained in narrow rows and thinned to improve air circulation and allow better light penetration. Weeds are very effective in reducing air movement therefore, good weed control within and between rows is important for improving air circulation within the planting.

Wild brambles, especially wild red raspberries, growing in the area should be removed. They can serve as a reservoir for the disease.

After harvest, remove and destroy all old fruited floricanes and any first-year primocanes that are infected. The best time to remove old and infected canes is after the canes go dormant in early winter or early spring before new primocanes emerge. If spur blight becomes an important problem in the planting, growers may want to consider the use of fungicide. Special fungicide sprays specifically for control of spur blight are generally not warranted.

For the most current spray recommendations, commercial growers are referred to Bulletin 506, Midwest Fruit Pest Management Guide, and backyard growers are referred to Bulletin 780, Controlling Diseases and Insects in Home Fruit Plantings. These publications can be obtained from your county Extension office or the CFAES Publications online bookstore at estore.osu-extension.org.

Figure 3. Disease cycle of spur blight.

This fact sheet was originally published in 2008.


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