Should I add diseased plants to my compost?

That’s a great question. According to gardenorganic.org.uk, some diseased plants can be added to your compost, however, plant materials suffering from soil-borne diseases such as clubroot and white rot should not be added to a compost heap.

Anything else can be safely composted in a hot heap. Diseases that don’t need living matter to survive, such as grey mould, mildews, and wilts, may survive in a cold heap.

But heat is not the only factor that will kill diseases: the intense microbial activity in a compost heap also helps to dispose of them. Some diseases, such as tomato and potato blight need living plant tissue to survive and will not last long without it. It is fine to add foliage suffering from these diseases to your hot or cold compost heap. If in doubt, leave it out. Problem materials can be sent to your local council green waste recycling facility where the composting methods are hot enough to kill any problem organisms.

that don’t need living plants to survive – grey mould, mildews, wilts – may survive in a slow, cool heap. But heat is not the only factor that will kill diseases – the intense microbial activity will also help to dispose of them.

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Can diseased plants be put in compost

Image courtesy of gardenseason.com

What are adelgids and how do I get rid of adelgids?

Conifers are a tree that bears cones and evergreen needlelike or scalelike leaves.  If you have conifer trees you may have to worry about Adelgids, which are are aphid-like insects that suck the sap from conifers.

Adelgid infestation close up zoomed in
woolly adelgid infestation Photographed by Michael Montgomery

Adelgids can cause distortion of shoots, affecting the appearance of trees. Yellow, winged adults leave galls in late summer and lay eggs on host plants. The nymphs soon hatch and overwinter close to buds. In spring these nymphs feed on plant sap but do not cause galls, maturing into light green wingless females. These females lay eggs covered in white waxy threads. The nymphs hatching from these eggs induce the galls when they feed at the base of needles. The galls contain numerous chambers within which groups of pale orange nymphs develop.

Adelgids only lay eggs, and never give birth to live nymphs as aphids do. Adelgids are covered with dense woolly wax. A complete adelgid life cycle lasts two years.

Adelgid nymphs are known as sistentes, and the overwintering sistentes are called neosistens.

Rain can kill adelgids by dislodging eggs and sistentes from trees.

So now that you know a bit more about adelgids, let’s discuss the reason why you’re probably reading this:

How do I get rid of adelgids?

The damage adelgids cause is often minor and can usually be tolerated, however, if you wish to remove adelgids from your plants, here are a few suggestions.

Adelgids can be difficult to kill with insecticides as they’re protected by waxy secretions. In addition it’s only feasible to treat adelgids on trees that are small enough to be sprayed thoroughly. It’s quite difficult to deal with  infestations on very tall trees.

hemlock wooly adelgid-bug macro microscope

The following insecticide information is from the RHS

  • Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Defenders Bug Killer, Ecofective Bug Killer (also contains fatty acids)), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Origins Bug Control) can give some control of adelgids. These pesticides have a very short persistence and so may require reapplication to keep adelgid numbers in check
  • More persistent insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Ultimate Fruit & Vegetable Pest Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) can also be used

The College of Agriculture, Food and Environment offers some clever ideas for controlling and eliminating adelgids including:

Spraying foliage with insecticidal soap or horticultural oil at the proper times during the HWA life cycle.

Using a systemic insecticide that moves with the tree sap and is consumed by the adelgids as they feed. 

There are three main methods for introducing insecticides including trunk injection. soil injection and soil drenching.

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