Soil pH may be cause of raspberry problems

  • Article by: NANCY ROSE , Contributing Writer
  • Updated: July 7, 1999 - 11:00 PM

QWe have 'Heritage' raspberries that are not doing well. Last year and this year they have had yellowish leaves and do not grow vigorously. We have fertilized them but the leaves are still yellowish. What else should we do?

AThere are several possible reasons for yellowing leaves and poor growth in raspberries. The two likeliest are unfavorable soil conditions or disease problems.

Raspberries prefer moist, well-drained, somewhat acidic soil. They do not tolerate constantly wet soil. If your soil has a very high pH (8 or higher), raspberries may show iron chlorosis (yellowing). In high pH (alkaline) soils, iron becomes unavailable for intake by the plant. The result is foliage that is yellowish except for the leaf veins, which remain green. If the yellowing pattern on your raspberry foliage matches this description you may need to acidify the soil. Have your soil pH tested to make sure.

(To know more about your soil, and what fertilizers or other additives your lawn and garden might need now or in the spring, have your soil tested. For a test kit, call your county extension office or the University of Minnesota Soil Testing Lab (612-625-3101). The lab will send a small bag for your soil and an information sheet. Return the sample and questionnaire, along with a check for $7.)

While it's better to change soil pH before planting by incorporating sulfur granules and peat moss, you can still modify the soil pH to some extent after planting. You can apply ferrous sulfate or apply acidic ferilizers such as ammonium sulfate or commercial formulations like Miracid. Follow instructions on the package for correct amounts.

There are also several diseases that can cause yellowing foliage on raspberries. Viral diseases are the most damaging. They can cause poor growth and declining fruit production in raspberries. Unfortunately, virus diseases are difficult to treat and may require removal of plants.

Raspberry mosaic virus is the most common of these diseases. It can affect most varieties of red raspberries, including 'Heritage.' Leaves of infected plants have a distinctive mottled pattern of green and yellow and are often puckered and misshapen. A ring spot virus of raspberries can result in poor growth and general leaf yellowing.

These virus diseases are spread by aphids feeding on the leaves or by a type of nematode (tiny wormlike creatures) in the soil. Controlling raspberry aphids by blasting the undersides of the leaves with water or using insecticidal soap or a labeled insecticide may help prevent spread of the disease, but it won't help plants already infected. Diseased plants should be removed and disposed of, not composted. Purchase new, certified virus-free raspberry plants and plant them in a different location, away from the old planting area.

Raspberries also are susceptible to some fungal diseases, but these would usually show up as discolored spots on leaves or canes, not yellowing of the foliage.

QI planted sugar pumpkin seeds this year and have three vines growing. They started blooming and I thought I was going to have a load of pumpkins but all the flowers came off. It almost looks like they were clipped off. Is this a bug, a disease or what?

APumpkins and other squash produce male and female flowers separately, though both appear on a single plant. Only the female flowers produce fruit. The female flowers have a swelling at the base of the flower, and that's what develops into the fruit if it's pollinated. The male flowers don't have a swelling at the base.

Usually there are more male flowers than female, and the male flowers generally start opening before any of the female flowers do. What you are probably seeing is an early flush of male flowers. They bloom, then the flower falls off, which might account for the clipped appearance. Keep looking for female flowers, which should appear soon. Squash need bees to carry pollen from the male to the female flowers, so make your yard bee-friendly. Plant plenty of different flowers and use pesticides limitedly or not at all. Bees are especially sensitive to the common insecticide carbaryl (Sevin is a trade name), so do not use this chemical during the pollination period.

QI had a number of different pepper plants but I lost the labels. I planted them but I'm wondering if there's any way to tell the hot peppers from the sweet peppers just by looking at the plant.

AWhile plants of individual pepper varieties look somewhat different, I don't think you can make an overall distinction between hot and sweet peppers just from the plant. Some of the small-fruited hot peppers, such as Thai hot, have smaller leaves, but jalapeño peppers are borne on bushy plants with fairly large leaves.

I think you'll have to wait until the peppers produce fruit. You may be able to tell the ones with obvious shapes, like the blunt, cone-shaped jalapeño or blocky sweet bell peppers, though long, tapered yellow peppers could be sweet bananas or Hungarian hot wax.

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