Thursday, December 19, 2019

Master Gardener: What’s wrong with a grapevine coated in powder - Press-Enterprise

Q: I have a 7-year-old grapevine that just started to produce fruit; however, the fruit looks like it might have some kind of fungus. It is coated with a white powder and has cracks. I heard that I should dust it with sulfur after it flowers – is this correct?

A: Powdery mildew is a common problem for grape growers. There are several different species of fungi that cause this problem, but the treatment is the same for all fungus species.

Powdery mildew fungus requires moist conditions to produce spores, grow, and infect grapevines. The spores can also remain dormant through winter, then reactivate when the weather heats up in summer.

Powdery mildew does not need moisture to live and grow once it is established. Symptoms include presence of a gray or white dust on the leaves, fruit, and flowers. It can also cause fruit to crack, ruining it.

Generally, the advice for preventing powdery mildew is to avoid planting susceptible varieties. Unfortunately, all grape varieties are susceptible.

The next best tactic is prevention. Make sure your grapevines are getting plenty of sunlight – at least six hours per day. Prune them to ensure adequate air circulation, and don’t plant them too close together.

The most effective treatment occurs before you see any signs of infection. Horticultural oil, Neem oil, sulfur, and Serenade are the recommended treatments. Sulfur should be applied after bud push and is only effective when applied pre-symptom. The other treatments can be applied after symptoms appear, but early treatment is most effective.

Do not apply oils within two weeks of applying sulfur.

Q: I have an orange tree that produces nice-looking fruit, but it’s dry on the inside. What causes this?

A: Citrus, especially oranges, will develop tiny cracks in the rind after being exposed to frost. These cracks are enough to allow the fruit to dry out, even though it looks fine on the outside.

Commercially grown oranges that have been exposed to freezing temperatures can only be used for juice for this reason.

Q: I have had problems with bugs getting into my flour, rice, and other foodstuffs. What can I do to get rid of them, and how can I prevent them from coming back?

A: Pantry pests can be either moths (Lepidoptera) or beetles (Coleoptera). When they are in the larval stage, they can be difficult to distinguish without getting up close and personal with a magnifying glass. I, personally, have never attempted to identify pantry visitors this way. My general rule is this: If your flour or rice is moving on its own, it’s time to discard it.

When you discover an infestation, you will want to act before it spreads. Remove the affected item(s) and discard in the outside trash. Carefully inspect all food in your pantry and dispose of anything that looks questionable. Re-usable containers should be thoroughly washed with hot soapy water.

Once you have an infestation, you should repeat your inspection several times until all the pests are gone. Label all packages with the purchased and/or opened date.

You may also want to think twice before buying that 50 pound bag of flour at your next trip to the warehouse store.

Have gardening questions? Email gardening@scng.com.


Looking for more gardening tips? Here’s how to contact the Master Gardener program in your area.

Los Angeles County

mglosangeleshelpline@ucdavis.edu; 626-586-1988; http://celosangeles.ucanr.edu/UC_Master_Gardener_Program/

Orange County

ucceocmghotline@ucanr.edu; 949-809-9760; http://mgorange.ucanr.edu/

Riverside County

anrmgriverside@ucanr.edu; 951-683-6491 ext. 231; https://ucanr.edu/sites/RiversideMG/

San Bernardino County

mgsanbern@ucanr.edu; 909-387-2182; http://mgsb.ucanr.edu/

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Master Gardener: What’s wrong with a grapevine coated in powder - Press-Enterprise
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