I'd scratch a tbsp. of lime around the base and water it in. If it is a mag prob then the lime will fix it. Alternatively a tbsp. of Epsom salts will give you the sulfur and the mag and its cheap. Epsom salts also is great for root development. In future grows try to grow in raised beds. Its better for drainage and promotes more O2 around the roots.
Honeydew is a sweet, sticky residue excreted from many sucking insects like whitefly and aphids. Ants love it.
There can be a secondary infection if you have enough sticky honeydew called Sooty Mold. Its not the same as the mold that causes bud rot and is just unsightly, black, ash like but you still want to avoid it.