Grape leaf problems

Asked July 7, 2020, 1:03 PM EDT

Local homeowner brought 2 samples of grapevine leaves. The first is yellow with green veins, chlorosis. I suspect Nitrogen deficienty, she thinks iron. She has been applying copper-ease, iron & sulfur. The leaves are staying the same, not worsening. Has never taken a soil test herself. When Conservation District tested years ago, the soil was different all over the vineyard (she has 18 vines.) I did recommend she do it again in the problem areas as this is only affecting some of the vines. The other leaf sample has brownish/orange spots. She has applied copper fungicide right before blooming and once a week since. She's also using Neem Oil. I'm not familiar with those products. She is beginning to notice tiny black spots on the grapes. I suspect Black Rot but due to the difficulty and possible severity of this, would like someone else to also take a look. Photos are attached. Thank you.

Codington County South Dakota

1 Response

It looks like the photos did not attach.

Chlorosis can be caused by a deficiency of iron or nitrogen, but more likely iron because our soils typically are a little alkaline (higher then 7). A soil test will reveal the acidity, as well as the availability of nitrogen among other elements. Once this is determined it will be easier to address the problem. Giving grapes nitrogen this time of year will produce a flush of growth and take away from the grapes maturing. It would also mean less available iron for that new growth so it could make things worse. Here is a list of testing labs.

If the soil pH is high, and nitrogen is in the normal limits, the next step would be to make the soil less alkaline.

Different cultivars of grape vines will react differently to the soil acidity. Mine have been growing for 12 years, mostly neglected and are just fine.

Here is more info on black rot

Fungicide applications should be timed correctly, proper sanitation is also paramount. We can continue this discussion once the photos are available.