Magnesium Deficiency of Cucurbit Crops
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Magnesium deficiency is more likely to occur on sandy soils with a low pH, especially in dry years. Sandy soils often have a low cation exchange capacity and may not contain adequate levels of magnesium. Deficiency symptoms are more commonly observed in muskmelon than in other cucurbits. Symptoms first appear as a yellowing between the leaf veins (interveinal chlorosis), beginning on the oldest leaves and slowly spreading to newer growth. Yellowed tissues may turn brown, die, and drop out, giving the leaf a shot-hole pattern. Magnesium deficiency usually appears during periods of rapid growth, when the fruit is enlarging.
Magnesium deficiency on muskmelon leaves.
(Photo: Terry Jones, University of Kentucky)
Management:
- Maintain the soil pH near 6.5.
- Soil test results should show at least 200 lb of magnesium/acre.
- Potential sources of preplant magnesium include magnesium oxide and dolomitic lime.
- If necessary, fertigate Epsom salts (magnesium sulfate) and magnesium oxide through a drip irrigation system.
- Avoid heavy applications of fertilizers containing competing cations (K+, Ca++, NH4++).
- Foliar sprays are generally ineffective in correcting significant deficiencies.