Chives possess allelopathic properties that suppresses many plant diseases. See: Alleopathic Plants
'Chinese chive plants ... significantly delayed and suppressed the occurrence of bacterial wilt of tomato.' 
'Intercropping with Chinese chives was not found to contribute to controlling the disease [Fusarium WIlt] ' 
Folk lore has claimed, and science has proven that pretty much any plant you grow near chives will benefit. The aroma of chives, although not quite as strong as its cousin garlic, masks the scent of neighboring plants which in effect makes them invisible to insects that would otherwise feed on them. , . Planted near roses chives prevent black spot. Chives are also helpful in suppressing mildew fungal diseases such as powdery and downy mildew.
Plant near apple trees, preferably at the base, chives are helpful in preventing apple scab and deterring some fruit worms.