Disease hosts

This is a good time of year to get a head start on weeding, as no-one likes weeding in hot weather. Leather gardening gloves or rigger’s gloves are great for weeding because they provide good protection from thorns, prickly stems, sharp edges of leaf blades, and insect or spider bites.
Weeds in the vegetable garden don’t just steal water and nutrients from your crops, many are also hosts to pests and/or diseases that can spread to your vegetables. By hosting diseases, weeds undermine your work at crop rotation to keep soil healthy.
Newly germinated weeds can be removed with a shuffle hoe, left on the bed surface, and covered with mulch. They will break down to return organic matter to topsoil. Small weeds that have not formed seed heads and are disease-free can be composted or put into worm farms. Larger weeds with seed heads must be removed and destroyed by burning, or soaking in water for an extended period, or disposed of in a sealed plastic bag. Remember the adage “One year’s seeds equals seven year’s weeds” – 15 years in some cases.
For gardening advice on removing troublesome perennial grasses and bulbous weeds, see my post on perennial weeds.

Nightshade (Solanum spp.)
The nightshade weeds are members of the same family as tomatoes, potatoes, capsicum and eggplant. Nightshade weeds (and Buffalo/Noogoora Burr) are hosts to Rhizoctonia fungi that can damage potato plants and tubers; cause collar rot in many plants, and cause damping-off in seedlings. They also provide a host to verticillium wilt that can affect a wide range of vegetables, fruit trees and ornamentals. Black Nightshade is a common weed in gardens. It grows to about 120 cm high, has groups of white (or purple-tinged) star-shaped flowers with a ring of 5 bright yellow stamens in the centre, and small green berries that blacken as they mature. Birds spread this weed by eating the berries.

Cobblers pegs (Bidens pilosa)
This weed is also known in Australia as ‘farmer’s friends’ because the barbs at the end of seeds allow the masses of seeds to cling to clothing and animal fur. Each plant produces hundreds of seeds and this weed can grow into dense stands that can quickly fill an entire bed. It is a host for root knot nematodes, tomato spotted wilt, and sclerotinia rot that can affect many crop plants. Remove and destroy these weeds while they are very small.

Herbicide damage

Broad-leaf weed killers that contain the pyridine herbicides have caused widespread damage to many gardens in New Zealand, the UK and the US in recent years, and these herbicides are now being sold in Australia.
Pyridine herbicides include aminopyralid, clopyralid, fluroxypyr, picloram, and triclopyr. They are only effective on broad-leaf plants, but the chemicals remain active in mulch cut from sprayed pastures and in manure from animals that have grazed on sprayed pastures until the chemicals are broken down by soil microbes. Of particular concern to home gardeners and councils that recycle waste into compost for agricultural and domestic use are the products containing aminopyralid, clopyralid and picloram because they are quite persistent in compost (particularly anaerobic compost), and residue from these herbicides can damage crops for up to 24 months.

Is it just me, or do other people think it is crazy that there is widespread concern about the future of food production in Australia, and all levels of government are advising us to recycle and store carbon, yet the Australian Pesticide and Veterinary Medicines Authority (APVMA) continues to register more and more of these herbicides that damage food crops, and little if anything is being done to warn the public of the risk in using mulches, composts or manures contaminated by these herbicides.
Although there are only two pyridine herbicides containing aminopyralid (Hotshot and Grazon Extra), the APVMA has registered 59 herbicides containing clopyralid, 54 containing picloram, 27 containing fluroxypyr, and 77 containing triclorpyr, and there are several more of these herbicides awaiting approval – an impossible list to remember when purchasing mulches, manures or compost.

The problem with Australian regulating authorities is that they regard the person who sprays the herbicide as the ‘end user of the product’ and any warnings are limited to product labels without any regard for the unsuspecting gardeners who, in good faith, purchase mulch, compost or manures contaminated with the herbicide, and who may not recognise the cause of the damage to their crops because they have not personally used any herbicides.

I am very grateful to Jo T. who has sent me a link to photos of damage to vegetable plants caused by aminopyralid. These may help readers identify this herbicide problem in their gardens.

If you are unfortunate enough to have garden beds affected by these herbicides, click here for treatment information.
See also Herbicide warning.

Further Information:
You can find Australian product names of these herbicides by going to APVMA’s Public Chemical Registration Information System page. Select herbicide and then type aminopyralid, clopyralid or picloram in the active constituent panel.
The NSW Government has been aware of the problems with these herbicides in Australia since 2005:http://www.environment.nsw.gov.au/resources/warr/SPD_ORG_ReduceRiskHerbCompost_FS.pdf
Jo has also provided a link to UK information about aminopyralid problems.

Soil pH too high?

A reader has added too much mushroom compost when preparing his vege bed. I am including his question and my answer here as over–adjusting soil pH can to be a problem for some gardeners.

I would really like your advice. I purchased some “premium garden soil” and added a lot of straw, lucern, manure and bagged mushroom compost thinking I was making fantastic vege garden soil. I since tested it and found it to be very high ph of 9-10. I think I added too much bagged mushroom compost. I added agricultural sulphur about 2mths ago but it doesn’t seem to be working or is very slow. After reading some posts above it seems it might be too difficult to reduce the ph to a normal level as the ph is way too high and all the organic materials may be acting as a buffer against the sulphur too. Do you think the soil will gradually come down or should I get rid of it and start again? Should I add more manure and just plant in it using a potting mix and hope that it comes down? Please help. Thanks for your advice.

You are correct in thinking too much mushroom compost is the problem because mushroom compost often has lime added to it before sale. For future reference, it is always a good idea to test the pH before deciding how much to add to garden beds, as too much can be a problem, as a high pH means that phosphorus is not available to plants and this makes it difficult to get your veges growing. Adding sulphur will help correct moderately alkaline topsoil but clay soils require 4 times as much sulphur as sandy soils, and it is almost impossible to bring alkaline soils back to neutral with one application.
You could try adding some cow manure (which is quite acidic) to the garden bed. This will reduce the pH over a couple of months because organic matter releases hydrogen ions into the soil as it breaks down. These displace the calcium ions from clay and compost particles and the pH gradually drops. If you don’t need all the bed in the next couple of months, you could grow a green manure grain in part of the bed area, slash it when knee high and dig it into the topsoil. As the green manure breaks down it will also help to lower the pH as well as providing a habitat and food for the microorganisms that keep soil healthy. Don’t worry, a little practice at preparing beds and you will be an expert.
If you want to get a few things growing before the pH of the bed has adjusted, you can add a rockmelon-sized amount of certified-organic compost to each seedling planting hole before planting the seedlings, or add some to a furrow where you will be sowing seed. One of the marvelous things that mature compost does is buffer roots from an unsuitable pH in surrounding soil. Hopefully, by the time the seedling roots grow into the other soil the topsoil will have a more suitable pH. Amgrow Organix is a good brand of compost to use – it has a pH of around 6.5 – perfect for seedlings.

CCA treated timber restrictions

I am concerned to hear that CCA treated timber has been used to construct garden beds and other structures in some school gardens, so it might be a good time to remind readers that the uses of these timbers have been restricted.
Since the end of March 2006, timber treated with copper, chromium and arsenic as a preservative (CCA timber) is not permitted to be used for garden furniture, picnic tables, exterior seating, children’s play equipment, patio and domestic decking, or handrails.
Problems with CCA treated timber
The restrictions on use were implemented by the Australian Pesticides and Veterinary Medicines Authority (APVMA) because they were “not satisfied that the continuing use of CCA for timber used in structures with which the public (and particularly children) are likely to come into frequent and intimate contact is safe“.
Common sense would dictate that the APVMA restrictions would also apply to garden beds (as they do to sand pits) because this timber can leach arsenic (a known carcinogen) into compost and soil for up to 20 years, and some species of food crops can absorb high levels of arsenic.
As young children have a tendency to put their fingers in their mouths, and tend to be less careful about washing their hands, they can ingest significant amounts of leached arsenic, a known carcinogen, from CCA treated timber. Children are, of course, more vulnerable to all pesticides because their organs are still developing and young children eat more food per kilogram of body weight than adults do.
The APVMA’s decision follows the phase-out for domestic uses of CCA treated timber in the US, EU, Canada, Indonesia and Vietnam, and restrictions to its use in Japan.
The regulations allow the use of CCA treated timber for ‘structural timbers’ and the timber industry has included retaining walls in that description. However, the APVMA Review (page 11) clearly states, structural timbers “where frequent contact is unlikely, and the level of exposure and risk, is low“.
Once installed ……..
Research by the US EPA (in 2005) found that penetrating sealants can reduce, but not eliminate, arsenic migrating from the treated wood. The data show sealants that can penetrate wood surfaces are preferable to products such as paint, because paints and other film-formers can chip or flake, requiring scraping or sanding for removal, which can increase exposure to arsenic.
More recent US research has found that arsenic levels on CCA-treated wood remained high for 20 years, and that timber had to be re-coated every 6 months, making the maintenance of this timber to reduce students’ exposure a tedious and expensive process. The only safe solution is to replace the CCA treated timber with one of the safer alternatives that are now available.
APVMA Review

Soil for Magnolias

Recently, Anthea wrote to me about the problem of growing her Chinese Magnolia where soil is alkaline.
I was just reading your article on changing soil ph and was hoping you could give me an idea on how to fix a problem I have with my magnolia x soulangeana.
I bought the tree approx 4 years ago and, although it has grown well and has good leaf coverage, it has never flowered. My thoughts at first was that it was still too immature to do so, but I have since discovered that the ph level of our soil is very alkaline (we live on the side of an extinct volcano towards the coast). Over the last year, I have been trying to reduce the alkalinity of the soil with a general garden sulphur, but this does not seem to have worked. Once again, no flowers/sepals this year. I have checked the soil ph again, and it is still as alkaline as it was a year ago. I do not want to be as drastic as to uproot the tree and replant in an acidic base soil as I am aware that magnolias don’t take kindly to transplants but I am at a loss as to what else I could do. Do you have any suggestions as to how to rectify this problem? I live in Mount Gambier in the south east of SA. Any help/advice would be greatly appreciated.

It is a long job to reduce very alkaline soil with sulphur alone Anthea, and when soil is very alkaline plants can’t absorb the nutrients they need to produce flowers (or fruit, in suitable species).

I would try putting some aged cow or horse manure on the soil surface around the tree (keeping it well clear of the trunk) after a thorough watering, and covering the manure with about 5 cm of organic mulch to keep it damp. As the manure (and mulch) break down they will release hydrogen into the soil. The electrically charged hydrogen ions will replace the calcium ions in the soil and the pH will drop. It won’t happen overnight, but it will happen. One of the problems on dairy farms is that the soil becomes quite acidic due to the constant manure deposits.

Then, when the tree is in leaf, spray the foliage with organic seaweed extract diluted to weak black tea colour. Seaweed is high in potassium that plants require for good flower formation, and it also contains a range of trace elements that plants need but can’t absorb from alkaline soils. This may be enough to assist flowering next season. I would spray as soon as leaves form and again in early summer.

By the way, volcanic soils are usually rich in nutrients and Plants usually grow well in them when pH is adjusted. As the pH problem is likely to affect your entire garden, it might be worth your while to invest in a pH test kit and and make annual adjustments to your soil where necessary.

Germination tips …

Last Saturday’s ‘Gardening Australia’ program made the claim that you won’t find the tip to use Epsom Salts to assist germination in any gardening books. That’s not true!
You will find that tip and lots of other tips for getting the best germination and growth from young seedlings in ‘Easy Organic Gardening and Moon Planting’ pages 132-136.
Epsom Salts is a fast source of magnesium for plants. Magnesium, as well as being an essential part of chlorophyll – the green colouring in plants, performs a range of tasks in plants including dissolving the germination inhibitor that coats seeds. Use a half-teaspoon of Epsom Salts dissolved in 2 litres of water to dampen seeds after sowing.

Herbicide warning

Before purchasing mulches or manures for your garden, ensure that they don’t come from pastures treated with a broad-leaf weed killer.
A relatively new herbicide (weed killer) ingredient, aminopyralid kills broad-leaf plants by disrupting plant cell growth. It does not affect grasses, but can remain active in them, and manures from animals that eat sprayed grasses, until it is completely broken down by composting or soil microbes.
Some readers may remember that, 16 months ago, I drew attention to the devastation this herbicide caused in UK gardens, rendering garden beds unusable for almost two years, after contaminated pasture was used as mulch, or uncomposted manures were dug into garden beds. UK residents were advised not to eat any produce from affected garden beds.
Despite extensive problems in the UK, and the fact that aminopyralid is highly mobile in soil, our Australian Pesticides and Veterinary Medicine Authority (APVMA) has approved herbicides containing aminopyralid under the names; ‘Hotshot’, ‘Starane’, and ‘Grazon’.
The APVMA Manager – Public Affairs told me that the APVMA requires products that contain aminopyralid to include on the label the following instructions: The herbicide is not be used on land to be cultivated for crops for up to 24 months. The herbicide is not to be applied to crops or pastures, which are intended to be cut for the production of compost, mulches or mushroom substrate to be used for susceptible crops or plants, as straw, hay or other plant material treated with this herbicide may damage the plants. Manure from animals grazing treated areas or feeding on treated hay is not to be used for growing broadleaf crops, ornamentals or orchards as injury to susceptible plants may occur.
However, these warnings do not help the many gardeners who are unlikely to ever see the herbicide label and, completely unaware of any potential problem, may inadvertently purchase contaminated products.
To test manures and mulch for herbicide residue, see: Manure and mulch warning update
If you are unfortunate enough to have beds affected by this herbicide, click here for treatment information.

Poor pumpkin crop

Mary’s pumpkin vines have produced some good fruits but a lot of pumpkins get black spots, shrivel up and rot while they are still small. Other vines have had very few or no female flowers, and she is puzzled as to the cause of these problems.

The squash family can also suffer from ‘blossom end rot’, where black spots form on the fruit opposite the stem – but this is more common on watermelons. A combination of factors causes this common problem of shriveling of immature fruits in plants of the squash family. Click here:
Squash melon and cucumber problems
An application of seaweed extract ‘tea’ can also help by strengthening cell walls, and helping to reduce plant stress.
Pumpkin vines make an enormous amount of growth for one set of roots, and plants will only mature the number of fruits that the root system can support. You can help avoid problems by encouraging the growth of auxiliary roots. See: Assisting root growth

If plants are not producing female flowers, nip the end off the long runners. Some varieties of pumpkins and melons tend to produce female flowers on side shoots. The cause of this is ‘apical dominance’ where the main shoot of some species of plants produces a strong hormone that deters the growth of side shoots. When the tip of this shoot is removed, growth is stimulated in the buds that form side shoots.

Perfect Christmas gift

Looking for the perfect Christmas gift for someone who enjoys gardening?

EasyOrganic_cover.inddThe new edition of my book, ‘Easy Organic Gardening and Moon Planting‘ would be an excellent choice. This book is not just about growing food – all your garden will benefit from organic cultivation. It has 500 pages packed with easy-to-follow guides and secrets on how to maintain good health in your whole garden so that all your plants become naturally pest and disease resistant, and more tolerant of climate change while saving water.
The monthly gardening diary of what to do when for all climate zones can be used with or without moon planting, and there are spaces in the diary for you to add personal notes and reminders. For more information about this book, see: Recommended reading.

Cara at WAHMania has a small quantity of stock and, for Australian orders placed before this Friday, books will be sent by Express Post to ensure that they arrive in time for Christmas. To order merely click on the ‘Buy the book’ panel on the right hand side of this page.

Horse manure

Magic1One of our SA readers wants to know what to do about the weeds that sprout from their horse manure pile, as she is concerned about spreading the weeds through her garden. She also has a problem with millipedes. Interestingly, manure and millipedes have a relationship because millipedes feed on decaying organic matter and they can lay their eggs in faecal matter. Millipedes are related to slaters. See Slaters and earwigs for controlling them in the garden.
Horse manure is often the easiest manure to obtain close to metropolitan areas. We have found horse manure to be a good source of plant nutrients and our miniature Shetland, Magic, works 24/7 to keep up supplies. Small amounts can be fermented in a bucket of water, then diluted, to produce a fertiliser tea for plants that need a boost.
But, adding uncomposted horse manure to the garden can encourage millipedes, slaters and earwigs. This is more common if you use sheet composting for the manure, a process of spreading a layer of manure on an unused garden bed, dampening it and covering it with mulch.
The best way to use fresh horse manure is to put it into the compost heap as it is a good source of nitrogen and generates a lot of heat, but there is a big difference between an active compost heap and a pile of horse manure. The manure should be mixed with dry ingredients such as straw, mulch, shredded newspapers, or dry leaves to create a good nitrogen to carbon balance. The heap should also be turned regularly to aerate the heap because aerobic bacteria require nitrogen, moisture and oxygen to work efficiently. When the compost heap is turned, newly germinated weed seeds get turned into the mixture and provide more organic matter for the bacteria to feed on. In its early stages, the heap should generate enough heat to kill off pathogens and seeds. As the composting process continues, the heap reduces in volume. As it gets cooler, you will occasionally see earwigs, slaters or millipedes in the mix but they are helping to break it down so don’t spray them with anything. When the organic matter reaches a favourable stage, earthworms move into the heap if it has contact with soil, and they digest the decomposing organic matter and turn it into worm castings. The final product, ready to be used on garden beds, is about one quarter of the volume of the original heap, friable, very dark brown in colour, and has a earthy, rainforest smell.
If you just leave horse manure in a pile to break down, it will tend to pack down and anaerobic (without oxygen) composting will occur. This is much slower, and can generate unpleasant smells. A lot of the nitrogen can be lost to the air and other nutrients can leach away when it rains.
To get horse manure to work even more quickly in a compost heap, tip it onto a hard surface and mince it a bit with the edge of a spade, because bacteria only work on the surface area of the ingredients. Producing more surface areas to feed on by chopping ingredients will greatly speed up the process.