I thought that whiteflies left a honeydew residue that could turn into fungus...Anyways, do you know a recipe for insecticidal soap?

Honeydew can develop into sooty mold. But that is no relation to powdery mildew and will not form on veggies....too short a time period involved. btw, sooty mold is harmless unless it develops to the point where it inhibits photosynthesis. And routinely spraying the plants down with water will prevent any build up of the honeydew in the first place.

Homemade insecticidal soap is not the same as horticultural/agricultural insecticidal soap and tends not to be as effective and can even create reactions with the plants it is being applied to. You want to find a detergent-free soap, like Bronners or other pure castiile. Use 5 tbsp of soap for 1 gallon of water. You can add a teaspoon of vegetable cooking oil to help with adherence. Shake thoroughly to mix and then spray. If this is too strong a formulation and causes a foliar reaction, reduce the soap by half. This is a contact pesticide only so you must spray when the flies are present and active, coating them thoroughly.

It is important to monitor your plants closely and start any treatments before the problem becomes severe. Severe infestations are far more difficult to control and can debilitate the plants beyond recovery.

Have you ever used Safer's Insecticidal Soap? Is yes, would it be effective with whiteflies?

Thanks for your help!

Safers is a completely acceptable product and is a true horticultural insecticidal soap. And if used correctly, is very effective against a modest whitefly problem.

Thanks! I’ll try to buy it

Do you know how I can treat the powdery mildew?

Powdery mildew on what?

On zucchini and cucumber leaves.

Also, would Safers be toxic?

Cucurbits - the zukes and cukes - are extremely prone to late season PM. I generally just remove the most badly damaged or infected leaves. PM typically results from high humidity (especially at night) and dry soils, so a deep soaking periodically at the root zone can eleviate a lot of it. Also spraying down the foliage will help. PM spores cannot germinate on a wet surface. I'd also recommend neem oil....which will address the whitefly issue as well (one product - multiple uses).

Safer's toxic to what? To you? Not at all, although I'd still wash any produce well to remove any residual.

Can I ask you one more question? Both my zukes and cukes have not produced any female flowers yet. Is this normal? (They have been producing male flowers for over a week.)

you have been such a great help!

It depends on the age of the plant.....getting kinda late in the season now (these plants have been producing mature fruit for at least a month or more here), but the production of almost only male flowers first (young plants) is very common. Females will follow shortly.

Note that washing plants to inhibit mildew needs to be done in the morning so that they do not remain damp overnight.