Our lemon bush is loaded with lemons, but some of them are covered with a black mold along with the stems, leaves, and branches.I can wash the mold off with a little bit of scrubbing. What can I do to prevent the mold from forming? Also, I’m noticing that a few of the lemons are an odd shape.
The odd shape lemons and the Black Mold are two unrelated problems both caused by two different pests.
The Black Mold forms on the clear, and sometimes sticky, secretions from sucking insects such as Aphids and Scale.
These insects suck the plant juices out of the tissue and then pass it through their bodies in the form of secretions that then drops to whatever is below.
Aphids are active on the new growth during the spring while Scale is present year round. There are several types of Scale, and they’re found on the leaves and older stems of the host plant. Also, it can be found to be a problem on Oleanders, Pyracanthas, Podocarpus, Cherry trees and Escallonias.
Horticultural and Neem Oil are safe, organic controls for Aphids and some types of Scale and it can be applied to citrus year round. Lemons tend to flower and have maturing fruit most of the year, so spraying is a bit of a challenge.
You'll have to pick a time when there are just a few flowers on the bush or be content with fewer lemons for a while. It’s easier with oranges, and other citrus as they have one primary blooming period. The oil sprays control the insects, but it does not clear or remove the existing mold from the vegetation.
It disappears in time. It is recommended to feed often with Citrus Food to encourage the new growth that in turns mask or covers over the unattractive foliage.There is an old saying certainly then applies this situation "Out of site out of mind."
Citrus Bud Mite (Eriophyes sheldoni) or herbicide damage are the primary causes of the funny looking of distort lemons. Non-selective herbicides, such as Roundup are not the problem. Instead, it would be a broadleaf herbicide usually used in turf for Dandelions and other weeds.
These products increase cell division to a rapid pace causing herbaceous plants to collapse and die. With woody ornamental plants like lemons you would see distortion in varying degrees; hence, the odd shapes.
Citrus bud mite is difficult to detect because the mites are so tiny they cannot be seen with the naked eye. 'Eureka' lemons and 'Washington Navel' oranges are the most common hosts for the mite, but all citrus may be attacked.
The mite has been a coastal problem, but it is starting to move inland. Oil sprays are the recommended control. It’s usually not recommended to do anything with a few affected lemons. However, in your case, you’ll get the benefit from the oil spray in controlling the other problems. The oddly shaped lemon are still usable so I would not discard them.