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Blight, mites, and spots, oh my!

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By Dennis Morgeson

Summer has begun according to the weather, but not the calendar.  Personally, I love the heat and humidity, but I know many of you don’t. But hey, that’s why we have four seasons.  There are several problems in the garden right now and if you read my article last week you know the big one is on tomatoes.

As many of you know, I live in Lebanon and last week we got an email from the university that late blight has been confirmed in Marion County on tomato and potato.  This wasn’t a shock to me as I had some infection on my own tomatoes two weeks ago.  What is important with this news was the infection on potato.  According to the vegetable specialists it meant the disease was overwintering here and may be a regular problem during the entire growing season for potatoes and tomatoes.  Usually we get late blight infections late in the season when the weather is cloudy, wet and cool.  On a positive note late blight doesn’t like hot weather and even more so hot dry weather and it looks like that is coming.  If you suspect you have late blight, bring me a sample or send me some digital pictures at dennis.morgeson@uky.edu..  You can keep late blight in check by picking off infected leaves, mulching around the plants, not overhead watering, and a must is a fungicide spray program.  Daconil, Mancozeb, and Maneb are the three fungicides that are labeled for home use on tomatoes.  You will need to spray the entire plant as long as conditions exist for infection and if you have diseased leaves.

Roses have developed black spot and powdery mildew quite a bit in the last few weeks and will need some help getting through this if you are growing hybrid teas and floribunda.  One of the best chemicals for homeowners is immunox a systemic fungicide that is pretty effective if sprayed regularly.  You can mix daconil, mancozeb, or maneb with the immunox to give the disease a one two punch.  Immunox will help stop additional infections and the others kill spores that are being released to cause additional infections.  As always, follow the label directions.  Also don’t overhead, water roses and mulch them well.

I saw my first Japanese beetle this weekend so be on the lookout for them.  They will be on the increase quickly now and will probably peak by mid July.  Sevin (carbaryl) is the most effective Japanese beetle control.  You can also hand pick them or knock them into soapy water in the mornings.  They can’t fly well early while there is a lot of dew and the weather is cool.

Spider mites are also coming out now and like many of the other insect problems they can become very bad, very quickly.  Plants with spider mites have a dull appearance because the mites suck the chlorophyll (green pigment) from the cells.  This takes water and nutrients from the plant as well as its ability to manufacture food through photosynthesis.  Spider mites are very hard to control while conditions are favorable which will extend into the fall.  There are several chemicals labeled for mite control however not many of them are effective long term.  If you have had recurrent problems in the past, you might want to invest in an actual miticide.  Avid and florimite are two very good ones but they are expensive.  Insecticidal soaps can help as they will kill the adults but the eggs will continue to hatch.  Spraying a fine hard mist under plant leaves will disrupt the mites breeding and reduce their numbers as well. Lastly there are all kinds of products labeled for mite control at the big box stores and garden centers and if you have never sprayed for mites, they will probably work for a while.  It is a good idea to spray different products so as not to allow the mites to become immune to a particular pesticide.   Lastly don’t spray sevin (carbaryl) on plants with spider mites.  The Sevin doesn’t kill the mites but it does stress them which in turn will cause them to breed more which will actually cause your mite problem to become worse.  I found this out the hard way several years ago.