We were at 8 weeks on our black bean plants beautifully making their way up the trellis, when we decided to treat the leaves with Neem oil spray. A number of holes had appeared in the leaves which we presumed to be the result of aphids. We applied the Neem spray at 6pm. Instructions on the bottle asked the user to spray so that leave was saturated, and that to be effective, entire plants needed to be sprayed. The following days, the lower leaves turned yellow and began falling off. Tested soil: pH of 7.8 (slightly alkaline), and moisture meter (which shows indications of dry, moist, and wet) has the needle pointing halfway between moist and wet. I'm thinking that the runoff of the neem oil in the soil causes inability of root system to take up iron, or nitrogen, or both. Going to add 2 teaspoons of vinegar to gallon of water for next watering, and going to spread coffee grounds to add some nitrogen to soil. Any other ideas would be greatly appreciated as it is disappointing to see the plants suffer this late in the season.

I hadn't heard of Neem meal until your post, so I looked it up. Apparently, Neem Seed Meal is what's left of the seed after the extraction of oil. Therefore, it shouldn't burn like the Neem oil does. Down to Earth says the meal "is an excellent way to strengthen root systems, improve plant immunity and balance nutrient levels in the soil". According to reviews, the downside is cost compared to other seed meals and an unpleasant Neem smell. But perhaps the benefits are great. I hope you report back on how it does for you. I'm especially interested if you think it helps with insect resistance. I might give it a try.

Thanks for the feedback, everyone! I'm sure the effects are also highly dependent on the strength of the emulsion. I will say this about horticultural oil, though... it doesn't cause post-spray stinkiness like neem does! I think I have a new go-to during the winter months when I have to co-exist with my trees indoors. I'll probably fall back to neem in the summer months. -Tom

The tops of all my sunflowers that I sprayed turn very light green never seen anything like this before Not sure what is happening but it was clearly without question caused by the spray. I'm trying to stay positive but there's no way something this odd and out of the ordinary happening the things I've grown for 10 years can likely be good