Aphids should disappear when temperatures rise

Q: I attempted to grow watermelons for the first time last summer and everything was looking good until it got hot. These tiny black specks appeared on the back of some of the leaves. I was told it was aphids but they weren’t sure. I hope you can see them clearly from the picture I’ve attached. Should I use insecticidal soap as recommended or something else? 

A: I tried to magnify the picture so I could see the black spots better. I could not see them clearly but whatever they were, it appeared that they were no longer a problem and the leaves seemed nice and healthy.

Aphids are cool-weather insects, so they should have disappeared when the heat hit. The big insect problems for you on watermelon would be aphids earlier in the season during cool weather, squash bugs shortly after planting and whiteflies (during the heat).

Yellow sticky traps can provide a method to determine if whiteflies are a problem . I will post a short video on my blog on how to make these .

Soap and water sprays are good but must be done about every three or four days and the underside of the leaves must be sprayed as well. Squash bugs are nasty and can be vacuumed or hand picked or delay planting by seed until after June 1. If you are hand picking or vacuuming squash bugs, then be diligent for about three or four weeks and keep the plants cleaned off every couple of days by hand until mid-June to avoid most of the problems with this insect.

Q: I’m sending you a photo of a leaf from my privet tree that has some kind of fungus. Can you suggest some fungicide ?

A: I think it is just a lack of good nutrition and perhaps a lack of adequate watering rather than a disease caused by a pathogen like a fungus. However, too much water applied too often can look similar to this.

A lack of water usually results in leaf drop in the early stages of stress with this tree. I will post your picture on my blog for readers to see your problem.

Japanese privet does much better in mixed landscapes than alone in rock mulch . They do not like soils that develop in a rock environment and have trouble picking up the right nutrients from these soils to stay healthy. Please be aware that this tree is not a desert plant so it will require more care .

Without soil improvement you might try giving it a better fertilizer. Fertilizers for trees and shrubs from manufacturers such as Miracle-Gro, Peters and Jobe’s will provide better nutrition than an inexpensive agricultural fertilizer. Add to this an iron product that contains EDDHA chelate (look at the ingredients).

Q: I have two cherry trees and one needs to pollinate the other. Can I plant both trees in the same hole to save space?

A: Yes, you can. Plant them about 18 inches apart, one on the east side and one on the west side of the hole. Try to pick varieties that are similar in vigor (how strong they grow) and on the same variety of rootstock.

I will warn you that sweet cherries are squirrely in our hot desert environment. They produce cherries in some microenvironments and not in others. They usually seem to do better in backyards that are somewhat protected (no strong winds) and have a more humid environment during pollination.

If you plant these two trees together, do not let them compete with each other. This means there will be a clear separation between the plants in their own half circle of canopy space .

These cherries must also bloom at the same time if they are to pollinate one another. Check your pollination charts to make sure they are compatible.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.

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