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Fielding Questions: Blossom end rot can hit zucchini

Q. Every year we have problems with zucchini. There are numerous little ones set on the plant but they stay about the same size, never getting bigger than 3 inches long. Many of them rot beginning with the blossom end until they are completely spoiled. Any ideas? – Gary and Elaine Hoffman, Ashley, N.D.

A. Blossom end rot is most commonly discussed with tomatoes, but it similarly affects summer squash like zucchini. It’s not a disease and does not spread. Instead, it is a physiological disorder caused by a lack of calcium in developing fruit.

Blossom end rot begins as a water-soaked, sunken spot on the blossom end (the end that isn’t attached to the vine). Zucchini may become a few inches long but never enlarge. Anytime movement of calcium into the plant is slowed, blossom end rot will likely develop.

It can be a sporadic or persistent problem, depending on what is preventing calcium from reaching the developing fruits. This deficiency can be caused by fluctuating soil moisture, excess soil salts or other fluctuating conditions during plant growth. It may also be confused with rotting fruit that results from the failure of female flowers to set fruit due to lack of male flowers or pollinating insects.

To remedy, locate in well-drained soil, mulch to keep soil uniformly moist and avoid fertilizers high in ammonium-type nitrogen, which ties up calcium. Avoid damaging roots from cultivating close to plants. Products marketed to spray foliage with calcium might work, and research is being conducted.

Other rots can begin on blossom remnants that cling tightly to fruits. When tiny zucchinis have started to elongate, gently remove the wilted, soggy remains of flowers from the fruit.

Q. I have a clump river birch tree that was very healthy until the past couple years when it showed signs of chlorosis.

Last year I treated it by incorporating iron and magnesium into the soil, applying as per instructions, including filling holes drilled around the drip line of the tree. So I was a little surprised that the tree is showing such bad chlorosis this year.

I wonder if I overdid it with the nutrients. But you mention in your recent article that there may be issues with plant’s ability to absorb the nutrients. – Mark Haen, Fargo

A. I doubt that you over-did the material. Iron deficiency chlorosis, as identified by veins remaining green while the remainder of the leaf turns yellow, is intertwined with cool, wet soil conditions and soil alkalinity. These conditions prevent plants from utilizing the normally abundant soil iron.

Iron products like you applied are “chelated,” in forms that are readily absorbed by plants. If iron-blocking environmental conditions persist from year to year, it is necessary to apply chelated iron as needed, often once or twice a season.

Foliar sprays of iron provide quickest results. Couple these with soil applications, which last longer. Although you treated the tree last year, continue again this season.

Q. We have a Prairie Magic apple tree but don’t know much about it. How big do the apples get? When is it ready for harvest? Anything you can tell us would be helpful. – Jeffrey Gellner, Fargo

A. Prairie Magic was introduced and promoted by Manitoba, Canada, as the best-tasting apple adapted to the northern plains and is currently among apples recommended by North Dakota State University. Fruit size is medium to large and ripens in mid-September, which is considered a mid-season apple. Taste is sweet, crisp and delicious.

Most apple varieties should spend the first 3 to 5 years producing branches and tree structure and strength, without expecting them to fruit. Do not fertilize the lawn around the tree, which can delay fruiting. Prairie Magic is great for fresh eating or cooking, with a long storage life up to 16 weeks if refrigerated.

If you have a gardening or lawn care question, email Don Kinzler at Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.