For gardeners on the east coast – don’t forget that it is a legal requirement in some areas to remove galls from citrus trees by the end of August. Gall wasps lay eggs in main stems or fruit stalks. This forms a swelling and gall wasp larvae weaken trees. As trees may be forming blossoms, delay in pruning may reduce next year’s crop. If you haven’t done so, check citrus trees (especially grapefruit and lemons) this week and prune off any galls before adult wasps emerge to lay eggs in new shoots. Burn affected prunings or dispose of them in a sealed plastic bag. See: Citrus gall wasp
Column 8 in today’s Sydney Morning Herald stated that Sydneysiders’ kitchens have been infested by fruit flies, stating that, “They emerge from fruit and hang around all summer”. The flies referred to are not fruit flies, they are the very small vinegar or ferment flies (Drosophila). Genuine fruit flies are kept out by fly screens. Vinegar flies emerge from fruit, tomatoes, etc. as grubs (larvae) and require pupation outside the fruit in order to complete their life cycle as a fly. If these tiny pests are a persistent problem, there must be a breeding ground nearby or the kitchen needs more regular cleaning.
Vinegar flies are attracted to the smell of yeast in fermenting organic materials and drains. To eliminate the problem:
- Do not keep fruit at room temperature in warm, humid weather
- Cover compost and garbage containers
- Regularly rinse out garbage containers
- Rinse beer and wine containers before recycling
- and treat drains with an enzyme product to break down thick scum where they can feed and reproduce.
Genuine fruit flies, the Mediterranean Fruit Fly (Ceratitis capitata) and Queensland Fruit Fly (Dacus tryoni) cause a lot of destruction in gardens. They require pupation in soil after the maggots emerge from fruit. To reduce the problem of genuine fruit flies, collect all fallen fruit, put it in a sealed black garbage bag and leave the bag in the sun for three or four days to cook the larvae (and encourage your neighbours to do the same). Never put infected fruit in the compost container.
Stressed plants attract pests and where you find pests you will also find beneficial insects that feed on pests. During extreme weather conditions you may notice some of these strange little creatures on various plants in your garden.
These are not pests – they are juvenile ladybirds
Both juveniles (larvae) and adult ladybirds eat vast amounts of aphids, various types of scale and mites. One species eats fungus, including powdery mildew. The white, fluffy species eat mealy bugs. They are difficult to distinguish from the pests they devour. Australia exports this variety of ladybird to the USA to help with their mealy bug problem.
These are some images of the pupa stage, just before adult ladybirds emerge. Ladybird larvae have an attachment at the end on their abdomens that allows them to stick to a leaf surface while they pupate.
Lady bird larvae often seek shelter from birds in the curled leaves that citrus leaf miners produce. Remember, if you decide to use chemical or organic sprays to treat pests that you will also kill beneficial insects and their offspring. There is only one species of ladybird that is not helpful in the garden: 26 or 28 spotted ladybird.
For lots more information about lady birds, see: Ladybird Field Guide
A reader wanted to know what what is causing yellowing of new leaves in her potted, dwarf lemon tree. From the photos she e-mailed, it does look like this tree has an iron deficiency, as yellowing is showing in the young leaves. This can be caused by a number of conditions:
a) potting mix (or soil) that is too alkaline from excess bio-char or calcium in the mix or fertiliser containing a lot of poultry manure
b) cold and wet soil or growing mix
c) if there is a build up of fertiliser salts from synthetic fertilisers, or
d) where there is an excess of potassium from synthetic fertilisers or over-use of seaweed liquid fertiliser.
The first thing to do is check that your pot has ample drainage. Large pots should not sit directly on a hard surface. While smaller pots usually have ample drainage holes around the sides at the base of the pots, large pots often have only one large hole in the base and this can easily become blocked resulting in poor aeration and/or a concentration of fertiliser salts if synthetic fertilisers have been used. Large pots should have pieces of tile placed under the pot to allow a small space between the base of the pot and the verandah or paving. If you notice crusting around the top of the soil line (fertiliser salts), flush the plant with clean water, once drainage has been improved.
The next step is to check the pH of the mix with a test kit. A suitable pH is important to all parts of your garden as the pH in soil or mix controls the availability of nutrients. Test kits are very economical to use and readily available from larger nurseries. If you find that the pH is above 7.2, you could repot the tree using an organic-registered potting mix as organic matter is an important source of iron. However, to do so may result in the loss of this crop of fruit.
The addition of flowers of sulphur (elemental sulphur) is the usual way to reduce pH in soils, but it is easy to overdo this in potted plants. You can apply iron chelates (the form of iron in organic compost) to the mix in the pot at the recommended rate. Citrus trees do not absorb iron chelates well through foliar spraying. Or, you can fertilise the tree with a weak solution of Multicrop’s Ecofish. This is an organic-registered liquid fertiliser that contains soluble iron and has a low pH, qhich will help to reduce the pH in the pot. Ecofish contains iron, manganese, sulphur and zinc (trace elements needed by citrus). Manganese deficiency is also caused by high pH or poorly-drained soil.
The warm, dry weather has enouraged this small native beetle (Monolepta australis) to move into gardens. As their common name suggests, these yellow beetles have a bright red stripe across their shoulders and a red spot on their wings. They arrive in a large swarm and choose one or two stressed plants to feed on. We have noticed that they frequently choose plants with white flowers. Although these beetles are only 6mm long, their sheer numbers enable them to skeletonise small to medium shrubs in a very short time before moving on to another property. Monoleptas are difficult to control because sprays that will kill the beetles will also kill beneficial insects visiting plants at the same time.
If the plant being attacked is not too large, you can get rid of these beetles by using a stick to knock them into a container of soapy water. Because of their fondness for the colour white, many beetles will drown themselves in a white container full of water left near the target shrub. (Don’t add soap to this water or it will kill bees that stop by for a drink.) The only way to protect your garden from attack by these beetles is to keep shrubs watered during dry spells, and keep the garden surface mulched to prevent moisture loss through evaporation.
Agricultural lime or elemental sulphur are recommended to modify soil pH to a range that suits healthy growth of particular plants. A reader recently asked me if “Lime Sulphur” was suitable to use around roses in her organic garden.
‘Lime Sulphur’ or ‘Lime Sulfur’ is a fungicide/pesticide formed from reacting calcium hydroxide (made from adding water to quicklime) with sulphur. It is usually applied when roses are dormant as it can burn foliage.
Hydrated lime is very reactive and should not be used where plants are growing. Lime Sulphur solution is quite alkaline (pH 10.5–11.5) and corrosive. Gloves, goggles, face masks and protective clothing must be worn as the pesticide is very irritating to the eyes, skin and respiratory passages. See the Material Safety Data Sheet for this product.
Plants are affected by diseases when they cannot get enough of the elements (including sulphur) they need for a healthy immune system either from inadequate fertiliser, or an unsuitable soil pH (because pH controls the availability of different nutrients to plants), or soil that is either too dry for the roots to absorb the nutrients, or is waterlogged and very acidic.
Although some sources state that Lime Sulphur fulfils requirements of organic gardening groups, the ‘Australian Certified Organic Standard 2010‘ lists Lime Sulphur as a restricted product and notes that it has a potential impact on beneficial insects.
My advice is to maintain a moderate amount of well-made compost in your topsoil, where compost holds all nutrients (including sulphur) close to plant roots; adjust irrigation and soil pH, and provide suitable amounts of complete organic fertiliser. In the meantime, if your plants have a serious fungal problem, I suggest you use Organic Crop Protectants’ organic-registered ‘Eco-fungicide’. It won’t damage your plants or your soil, and it is kind to beneficial insects.
Cabbage white butterflies have had a lovely time with my broccoli this year. There are several conditions that make brassicas very attractive to these pests and the brown cabbage moth. See Cabbage white butterfly.
My problem was that I inadvertently added some very alkaline compost to that area of the garden, (See recent post on compost pH) and it is taking a while for the soil to get back to a neutral pH.
After spending a week or so removing eggs, squashing tiny caterpillars, or feeding larger ones to the chooks, I remembered a tip someone gave me long ago to deter these pests but have not needed to use before. The tip was to slip the plastic clips that seal loaves of sliced bread onto the edge of some of the Brassica leaves. White seals to deter the C W butterfly and beige ones for cabbage moth. The theory being that the adult butterflies and moths will “think” that eggs are already being laid on these plants and they look for another food source for their larvae.
My broccoli plants are looking healthier already and I have not found any more eggs under the leaves, but I don’t know if the seals are working or the pests are no longer present in our area. Has anyone else tried this tip?
Nematodes that damage roots in the vege patch, are minute worm-like creatures, also known as eelworms. The female nematodes penetrate plant roots causing lumps to form on the roots, which affect the water-carrying ability of the roots. (These are not to be confused with the nitrogen–fixing lumps that form on the roots of legumes, see Fixing nitrogen). Root knot nematodes are more likely to occur in warm climates in soils that are low in organic matter, especially where a proper crop rotation has not been practiced.
Each female nematode can lay up to 2000 eggs, and numbers can multiply quickly. Give affected plants a foliar feed of seaweed extract tea. Seaweed contains plenty of potassium that helps to strengthen cell walls and improves plants’ resistance to pests and promotes root growth. Remove all weeds. Some weeds are hosts to these pests and can transfer viruses to plants.
Affected plants must not be allowed to become water-stressed. Badly affected plants will have to be removed. Make sure the soil is damp so that soil clings to the roots. Place plants (with attached soil) into a garbage bag. Seal the bag, leave in hot sun for a few days, then place it in the garbage. Do not compost these plants. Once the crop is harvested, proceed with methods for prevention (see below).
Allow 3 years between growing any member of the tomato/potato or melon/cucumber families in the same patch of soil. During this break, grow a green manure that is a ‘bio-fumigant’. ‘Bio-fumigants are green manures that release a gas that is toxic to nematodes. They are grown to knee height and chopped up and mixed through top soil, then covered with mulch. Green Harvest have seed for BQ Mulch (sown in cooler months) and cowpea (sown in warmer months) that control nematodes. Indian or brown mustard (Brassica juncea) and non-GM rapeseed (Brassica napus) are also effective bio-fumigants. Forget marigolds, they are more effective against northern hemisphere nematodes. During the 3 year break, brassicas or corn can be grown in the treated bed, if you have limited garden space.
When preparing beds, add a 5 cm layer of organic compost to the bed surface and cover it with organic mulch. Beneficial organisms in compost are pest nematode predators, and mulch keeps compost damp to allow microorganisms to work on restoring soil to health.
A reader has asked about powdery mildew on zucchini plants and fungus-eating ladybirds:
Hi. Wonder if you can sort this.
1. Most fungi need moisture and organic material. This seems to be supported by my zucchinis which seem to get worse powdery mildew when I get water on the leaves. I have read that they like dry weather. Is there evidence for either opinion?
2. Some people say that the ladybirds that feed on this mildew spread it by carrying spores, others reckon they are a controller, eating the fungus down. What is the evidence please for either of these? Many thanks, Barb
Powdery mildew is likely to occur on stressed plants in humid weather when temperatures are between 11-28° C. and, once established will continue to affect the plants even if weather becomes dry. Avoid wetting leaves whenever possible Barb. However, because they like low-humidity weather, it doesn’t mean that they are drought tolerant. Zucchini and some other members of the cucurbit family (melons and squash) produce a lot of foliage and need plenty of water and fertiliser. An efficient way to water this group of plants without wetting the leaves is to put a large drink container (with the base and cap removed) neck downwards near the roots so that all the water goes directly to the root area where it is needed, (see photo). Keep topping up the container until it empties slowly.
The yellowish ladybirds with 26 or 28 spots are the only pests of the ladybird family. They eat the leaves of stressed plants of cucurbits. The beneficial fungus-eating ladybird and larvae can be clearly distinguished from the pest in the photos below. From the far left is the ‘Fungus-eating ladybird’, then the leaf-eating ’26 spot Ladybird’ that damages plants. Next is the larva of the ‘Fungus-eating Ladybird’, which also eats fungus and, last of all is the prickly larva of the ’26 spot Ladybird.
Rather than blame the fungus-eating ladybird for spreading the disease, gardeners should check that their plants have sufficient water and nutrients to avoid stress, and the soil pH is suitable for them to absorb what they need for healthy, disease-resistant growth. Also see Powdery Mildew for treatment of this disease.
If new leaves on Camellia plants become thick and very pale green or pink, and the underside of the leaf starts becoming white – the plant is suffering from ‘Camellia leaf gall’. This is a fungal disease that affects tender new growth of Camellia sasanqua (and sometimes Camellia reticulata), especially in very humid or wet, shady conditions. Fungal diseases are a sign that growing conditions are stressing your plants and their immune system is compromised. There is no organic or chemical treatment for this disease. However, an application of seaweed extract tea will help to strengthen the cell walls of the affected plants and make them more resistant to disease.
But, first the affected growth must be removed, preferably before the undersides of leaves develop white spores. You will need a baked bean tin containing about 5 cm of methylated spirits to sterilize secateurs blades, and a large garbage bag for the prunings. Prune off all affected growth (swish the open secateurs in the spirits often while pruning) and place it directly into the garbage bag. Also collect in the bag any fallen leaves as they can harbour the fungal spores that will activate this disease again when conditions are suitable. Seal the bag and put it in the garbage if you are unable to burn the leaves. Do not compost them. Then give the soil around the plants a drink of seaweed extract at the recommended strength, and protect the soil surface with 3–5 cm of fresh mulch. Make sure your camellias are watered when the top centimetre of soil is dry, but afford watering the foliage. Also give the plants an annual application of compost or complete organic fertiliser and seaweed extract tea in late winter.
See below, how affected new growth appears, and close-up of affected leaves.