As one of the most popular fruit crops, raspberries are also frustrating, as they develop problems on the fruits and canes. Unless problems are diagnosed and treated, the harvest is often a dismal failure. Before giving up, try to solve potential problems.
Keep in mind there are two types of raspberries. Single-crop berries produce fruit on wood that grew last year. Ever-bearing types produced their spring crop on last year's wood and their fall crop on this year's growth. Foliage produced on last year's canes never looks as good as foliage growing on this year's canes. These differing growth habits may confuse some gardeners, as they expect all canes to look and produce the same.Many maladies can be attributed to a natural tendency to stop producing after the normal growth season. Both single-crop and ever-bearers stop producing during the hot, dry, midsummer. Ever-bearers have not yet started producing their fall crop.
Fruit damage from attacks by insects or diseases or from water and nutrient deficiencies or excesses is common. Fruits can be misshapen, dry and crumbly, discolored or chewed. Many symptoms have several causes, so identify the problems before trying to control them. The most common maladies follow.
Drought is a frequent problem. While raspberries don't like wet feet, they prefer cool, moist conditions. Lack of water causes dehydration of the fruit and the plants.
Insects or viruses can cause misshapen fruit. Several bugs feed on raspberries, resulting in unevenly developed fruit. Individual berry drupelets are sunken and misshapen, while adjoining drupelets appear normal. Tiny black sap beetles also feed on ripening fruit. They damage the entire berry as they feed to extract the sweet juice. The only solution to insect problems is to watch for the insects when they appear and wash them off or apply a preventative spray. Since damage often happens as the berries are ripening, malathion, pyrethrum or rotenone are the only products you can use with a short enough preharvest interval.
Spider mites attack during hot, dry weather. Plants get a gray, dirty appearance and webs on the leaves. Wash them with a strong stream of water, or spray insecticidal soap or Kelthane.
Yellow jackets attack raspberries all too frequently. They chew the fruit for food and water. This problem is worse during hot, dry weather or on fruit that is over-ripe.
Crumbly berries are usually small and fall apart easily. This common complaint is usually caused by inadequate nutrition or viral infections. One common disease, raspberry leaf curl virus, causes small, crumbly fruit. It also causes pronounced downward and inward curling of the leaves and severe dwarfing of the canes. This, and several other virus diseases, can cause extensive damage to raspberries. Viral diseases are inside the plant and have no chemical controls. Replanting certified virus-free plants in a new location is the only alternative.
Powdery mildew or rust can damage fruits and plants but are not usually serious. Powdery mildew produces a white film on the berries and on the leaves of affected plants. Rust produces orange dust on the back of the leaves and occasionally on the fruits.
Sunburn causes individual drupe-lets to turn white, hard and shriveled. It is common at high elevations and is most serious on the south or west side of the rows and individual berries.
Iron chlorosis produces yellow leaves with green veins. It is most prevalent on heavy clay with a high pH. Reduced watering and treating with iron chelate is the best solution. Iron chlorosis occurs in most raspberry patches to some extent each year.
One of the most common and distressing problems this year is wilting and die-back of the canes. If only the tips are affected, raspberry cane maggots are the culprit. They burrow in the pith and tunnel down the cane. Control this pest by pruning off below the damaged area and destroying the prunings.
Crown borers cause the entire cane to die by tunneling and girdling as they feed. These pests enter in the spring and can be par-tial-ly controlled by preventative sprays at that time. The only control at this time is to remove and destroy the affected canes.
Cane die-back may also be a result of verticillium wilt or phy-to-phera root rot. These diseases usu-al-ly cause the entire plant, and often surrounding plants, to die.
In spite of the many potential problems, raspberries remain a highly prized, delectable treat. Most problems are preventable with good cultural practices and attention to problem pests. Raspberries usually look their worst in the heat of August, so be patient and look forward to better crops when the weather cools.