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Diagnostic Tidbits (Week of July 1) - Jul 9, 2012

by UW Extension Plant Health Clinic Team

Listed below are this week's plant diagnostic and growing tips from the Plant Health Clinic team.

July 6, 2012:

Question: Why are my tomatoes turning black on the bottom?

Answer: This is a condition called Blossom End Rot. We often see this during hot, dry weather just like we've been having. It is caused by not enough water and calcium being taken up by the roots to the growing fruit. When the soil is dry about an inch down, water the plants deeply and evenly. Check daily during this hot, dry weather. It's best to water the base of the plants rather than over the tops and early in the day rather than in the evening. A layer of mulch will help keep the soil from drying out. If the problem is severe, apply a fertilizer low in nitrogen but high in superphosphate, 4-12-4 or 5-20-5, following application directions. Remove affected fruit. Do not apply insecticides or fungicides.

Tomatoes will not set fruit and flowers may drop in extremely hot weather but will recover as temperatures cool down.

Question: What has caused my paper birch to have yellow leaves that are dropping as if fall is here?

Answer: Laura Jull, UW Extension Woody Ornamental specialists, suggests that both river birch and native paper birch, even more so, are sensitive to drought stress.  This stress can be an accumulation of years where root systems may have been reduced or failed to thrive lessening their ability to take up necessary iron that gives leaves chlorophyll that healthy green appearance. Adding to this problem for much of our area is that our native bedrock is dolomite limestone causing soil pH to be above 7 which are less preferred by birches. The necessary iron is often present in the soil but the plant is unable to up-take-it. In severe drought stress conditions, birch will drop their leaves to try to reduce their water loss that evaporative transpiration causes. Mulch, weed, water and possibly a soil test for pH are in order.  The soil pH can be changed with an on-going long term continuous effort that few are willing to conscientiously take on.

Question: When should I harvest my garlic?

Answer: If the leaves are 1/3 brown, start testing if they are ready by carefully digging down to the top of the garlic and seeing if one is large enough. In any event, if the 2/3 of the leaves are brown, dig (not pull) up your garlic, brush off the dirt and hang in your garage. Do not leave out in the sun! Leave the roots and stalks on the bulbs and in three to four weeks, they should be ready to use. Softneck varieties of garlic can be stored for 6-8 months. Check periodically to make sure it is not going soft or sprouting. Hardneck varieties may dry out, sprouting or go soft within 2-4 months. Keeping hardnecks at 32 degrees sometimes helps them survive for up to 7 months without deteriorating.

If you're bugged by garden pests or would like some free gardening advice, get your horticultural questions answered by the UW Extension Plant Health Clinic team located in the lower level of the Visitor Center and at the Brown County UW Extension office. Check out our website for Plant Health Clinic hours and contact information.

UW Extension Plant Clinic Staff members – Vijai Pandian, John Hermanson, Lynn Clark, Dan Mitchel, Sue Roulette, Vicki Warden, Ritalyn Arps and Ryan Sievert


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