Monday, September 6, 2010

FAQ: Why do my grapes fall off the vines?

Q. I have Muscadine vines that have, after many years, covered my arbor.  It's about 12' x 18' x 8' high.  The soil is very poor,  yellow sandy soil.  I have 6 or 7 plants planted around the perimeter which now cover the top.  I give each each plant 4 or 5 cups of 10-10-10 fertilizer in February and I give them a lesser amount in June.  I have never pruned these vines, but I intend to this February.  I generally do not water them, except in very dry weather.  This arbor does not get full sun, probably one side gets morning sun and the other side gets afternoon sun.  My problem is, I get a good stand of fruit, but the fruit falls off when the grapes are very small.  I got like two very small grapes that actually ripened.  Also, I noticed some of the leaves were being eaten by something very small.  I never could see the culprit.  Not all over the arbor, just here and there.  Would you have any idea why my grapes fall off the vines and what should I do about these "bugs" eating the grape leaves?

A. I'm not sure exactly why the grapes are falling off, but if they fall off after your June fertilizer application, that could be the reason.  Ideally, your vines should receive full sun to produce higher yields, but they don't, so there's no sense in discussing that.  Muscadines are native to wooded areas anyway.  They don't naturally grow in open fields.  Excess nitrogen can cause fruit drop.  I believe this is the problem.  You probably don't need to fertilize them in June.  There may be another problem, perhaps a micro-nutrient deficiency.  Extremely dry soil conditions can also cause fruit drop, but I suspect that it's related to fertilizer application.

It sounds like the bugs (or whatever) that are eating some grape leaves are not causing a significant problem.  Some sort of beetle may be the culprit, but I wouldn't worry about it unless the problem becomes severe.

Your vines should be pruned annually, so it's good that you have that planned for this winter.

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MrsSW said...

John - are muscadines slow-growers?


GoGardenNow said...

Muscadines aren't slow growing. For best results, train to grow on a single-wire trellis about 4' high. Plant vines 20 feet apart. The trellis should be sturdy. The vine should reach the wire by the end of the first growing season. By the end of the second growing season, the arms should reach 5 or more feet in each direction. The arms should extend 10' in each direction by the end of the third season.