Control of Pests and Diseases

The most important principle of organic gardening is based upon taking care of the soil’s needs which provides the foundation for a complex ecosystem, including the plants we grow for food.

Maintaining healthy soils with a plentiful store of nutrients and sufficient moisture retention will provide your vegetables their best opportunity to grow healthy and strong.

Any slowing of plant growth due to lack of nutrients, moisture, or sunlight will lower natural immunity and create opportunities for disease or insect pests to establish themselves.

Companion Planting

Heavy feeders like sweet corn and squashes are frequently planted alongside nitrogen fixing legumes such as beans or peas.

This offers substantial protection to a soil’s nutrient profile, particularly its ongoing ability to break down and absorb organic soil additives such as dried manure, seaweed, and pea straw.

When cabbages, broccoli and related plants are interspersed with rows of onion, they are less prone to caterpillar and other larval infestation.

This is principally due to the onion’s stronger scent and its capacity to confuse or deter cabbage moths.

Various culinary and medicinal herbs have gained reputations for their insect repellent properties.

The complex aromatic oils of garlic, cloves, basil, lavender and sage will discourage aphid, fruit fly and other insects from attacking vulnerable species like citrus, rose, lettuce, and stone fruit.

Experienced gardeners will commit themselves to few rules and even fewer certainties with companion planting.

Most of us need to experiment with several approaches and will usually discover that success depends upon location, soil condition, and other factors in addition to the combinations themselves.

Bearing this in mind, it is good practice to keep detailed records of each attempt so that similar conditions can be repeated whenever a successful outcome is achieved.

Crop Rotation

The best way I know of keeping pests and diseases at minimal levels in your vegetable garden is to plant your vegetables based around crop rotation.

Crop rotation is about planting groups of similar vegetables together in a different part of the garden each year.

It's important to do this because different crops like different soil conditions.

Sweet corn and pumpkin love a rich organic soil, but the same soil conditions would make carrots and other root crops fork because of the higher nitrogen needed.

Pests and diseases tend to affect vegetable groups and will often remain in the soil for years.

But by following a rotation system these pests and diseases can't build up in the soil.

The length of a rotation system can vary from 3 to 8 years.

The longer the better. But this can be difficult with the size restrictions of the average backyard.

3 year rotation plan for a small garden in 40 cm pots

Here's a method based on a 4 year rotation. You simply move each crop anti clockwise through a cycle of 4 years.

crop rotation

Should you wish to go to 5 year cycle , simply split the grouping of root crops and onions ( alliums )- make them a separate bed.

Similarly if you wish to go to 5 , make another bed for brassicas and legumes.

I operate on a 6 bed rotation system as follows:

1. Alliums

2. Legumes

3. Brassicas

4. Roots

5. Cucurbits

6. Solariums

Greens such as lettuce and rocket can be grown anywhere to fill space. They do not need a separate group.

So based on this system , my garden would look like this over 6 years:

Bed 1 Bed 2 Bed 3 Bed 4 Bed 5 Bed 6 Yr

Leek

Garlic

Onion

Broad Beans

Peas

Beans

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

Carrot

Beetroot

Parsnip

Pumpkin

Squash

Cucumber

Sweet Corn

Tomatoes

Capsicum

Peppers

Eggplant

1

Broad Beans

Peas

Beans

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

Carrot

Beetroot

Parsnip

Pumpkin

Squash

Cucumber

Sweet Corn

Tomatoes

Capsicum

Peppers

Eggplant

Leek

Garlic

Onion

2

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

Carrot

Beetroot

Parsnip

Pumpkin

Squash

Cucumber

Sweet Corn

Tomatoes

Capsicum

Peppers

Eggplant

Leek

Garlic

Onion

Broad Beans

Peas

Beans

3

Carrot

Beetroot

Parsnip

Pumpkin

Squash

Cucumber

Sweet Corn

Tomatoes

Capsicum

Peppers

Eggplant

Leek

Garlic

Onion

Broad Beans

Peas

Beans

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

4

Pumpkin

Squash

Cucumber

Sweet Corn

Tomatoes

Capsicum

Peppers

Eggplant

Leek

Garlic

Onion

Broad Beans

Peas

Beans

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

Carrot

Beetroot

Parsnip

5

Tomatoes

Capsicum

Peppers

Eggplant

Leek

Garlic

Onion

Broad Beans

Peas

Beans

Brussels Sprouts

Broccoli

Cabbage

Cauliflower

Kale

Carrot

Beetroot

Parsnip

Pumpkin

Squash

Cucumber

Sweet Corn

6

Common Pests and Diseases affecting vegetables in Tasmania and other cool climate regions

A

Aphids

B

Blossom End Rot (Tomatoes)


C

Caterpillars

Cabbage Moth

Yates Pest Control for Cabbage White Butterfly and Cabbage Moth

Chocolate Spot botrytis fabae ( Broad Beans)

A fungal disease which attacks Broad Beans and looks like the leaves have been dusted with chocolate powder. The stems may also be affected. It is favoured by acidic growing conditions, lush growth and damp spring weather. Winter-sown crops are more susceptible. The crop will be reduced and the plants may die if the infection is severe. The beans are still edible, but the pods may be discoloured.
Affected plants should be burnt at the end of cropping. Space seed or plants well apart when planting and do not use large amounts of nitrogenous fertilizers.

Codling Moth (Green Harvest)

Club root (Brassicas)

Club root (Plasmodiophora brassicae), a nasty fungus, infected the roots, causing them to swell asymmetrically. The swollen roots cannot absorb water and nutrients properly—before long, you'll be reading the plant its last rites.

What must you do right away? This is no time to be patient. Club root is a persistent and damaging disease that afflicts all the members of the brassica family, which also includes Brussels sprouts and kale. You need an aggressive plan to stop it from spreading through your soil.

Dig up infected plants. Once you've identified a plant with club root, carefully dig around the infected area and gently remove the entire root system from the soil so as to prevent the clubs from breaking up and potentially releasing thousands of spores.

Discard (don't compost) the infected plants.

How can you prevent it from returning?

D

Damping Off Disease

This is a disease that causes newly emerged seedlings to die.

It attacks the stem at the soil line, pinching it off.

Sometimes a barky collar forms first.

Damping off is encouraged by very moist soil, by poor circulation and also by high temperatures or high levels of NPK.

Downy Mildew

This disease attacks many vegetables and grape vines in wet, humid weather.

Conditions for its spread in gardens are a rainfall of 10mm or more at a temperature of 10 degrees Celsius or more over a 24 hour period.

Oil spots initially appear on the top surface of the leaves.

This is the primary infection and is introduced by rain splash from the soil.

The Downey Mildew spores which over winter in the soil become active given the above conditions.

If further rainfall occurs after these oil spots are observed, a secondary infection is most likely to occur with fine white fungal hairs observed under the leaf surface.

Severe leaf damage and florescent infection leads to berry deterioration.

The conditions experienced in Tasmania during the Spring and early Summer of 2010 were ideal for the spread of this disease and much infection occurred.

Treatment: Initially, leaves with oil spots should be removed entirely from the vineyard.

Pre infection sprays should be applied.

For grape vines Coppox can be used as a deterrent in the early part of the season every 10-14 days.

During conditions that promote the spread of Downy Mildew, pre infection spraying should be done every 5 days as new growth prior to flowering is rapid.

Therefore every few days a new covering of copper is needed to protect any new green material on the vines.

Pre-infection fungicides (protectants):

These protect the vine by preventing infection.

Many belong to the Group M fungicides and are not systemic (phosphorous acid and fungicides in Groups 11 and 40 are exceptions).

The non-systemic (or contact) fungicides provide a protective barrier on the surface of the foliage where they stop the spores germinating.

Since downy invades through the stomates, apply contact fungicides to cover the undersides of leaves - the most difficult place to spray.

They must be re-applied prior to an infection event if there is sufficient growth of leaves or of developing berries.

Apply the sprays as close as possible before infection.

Access to forecasts of downy mildew events will help time these sprays best.

Post-infection fungicides (eradicants):

These are sometimes known as systemics - but note:

some pre-infection fungicides are also systemic.

The post-infection fungicides kill the pathogen inside infected tissue if they are applied at the right time.

They do not eradicate the disease from the vineyard but, being systemic, they are quickly absorbed into the sprayed foliage and are rain fast within 2-3 hrs of spraying.

Because Ridomil is usually mixed with mancozeb it simultaneously provides a protective shield against new infection.

The post-infection fungicides are more expensive but are able to 'eradicate' the downy pathogen from within infected tissue.

Consequently, apply these fungicides only when needed and then, as soon as possible after an infection and before oil spots appear i.e. in warm conditions, within 5 days post-infection.

Like all fungicides, good coverage is important.

The post-infection fungicides include Ridomil Gold® (a Group D fungicide) and phosphonate e.g. Foli-R-Fos® (Group 33).

Because resistance to Ridomil has been reported, Australian management strategies recommended only 1-2 applications per year.

In vegetables:

 

E

Enation (Peas)

A common disease of peas.

Causes warty looking leaves and pods.

Usually plants succumb to enation when the weather turns warm.

F

Fusarium Wilt ( Tomatoes)

Solanaceous crop plants (tomato, potato, pepper, and egg- plant) may be infected at any age by the fungi that cause Fusarium wilt and Verticillium wilt.

The wilt organisms usually enter the plant through young roots and then grow into and up the water conducting vessels of the roots and stem.

As the vessels are plugged and collapse, the water supply to the leaves is blocked.

With a limited water supply, leaves begin to wilt on sunny days and recover at night.

Wilting may first appear in the top of the plant or in the lower leaves.

 

The process may continue until the entire plant is wilted, stunted, or dead.

Tomato and potato plants may recover somewhat but are usually weak, unthrifty, and produce fruit of low quality.

Peppers typically collapse rapidly and die.

Fusarium and Verticillium wilts are rarely significant in field grown tomatoes due to the widespread incorporation in tomato cultivars of genes for resistance to the pathogen.

However, the resurgent interest in planting "heirloom" tomato varieties which do not carry resistance genes has resulted in increased incidence of Fusarium and Verticillium wilts.

With fusarium wilt the whole plant wilts, rotted at the base of the stem and stems may be cracked.

In mild cases the plant may just grow slowly or be pale and stunted.


Fusarium wilt is a soil-borne fungus.

Try covering the soil before you plant out tomatoes with clear plastic sheeting for three weeks to kill off spores in the soil.

Look for tomato seedlings that say they are resistant to fusarium wilt.

Some of the old fashioned varieties are very susceptible to it.

G

Grape Vine Caterpillar

This caterpillar belongs to the Grapevine moth.

It can cause severe damage to vine canopies if number are large, resulting in damage to the fruit quality through lack of sugar production.

Dipel is an effective control if sprayed in the cool of the evening.

Dipel contains Bacillus thuringiensis, or Bt for short, it is highly effective and selective against most species of caterpillars including lawn armyworm syn.

lawn grub, cotton bollworm, cabbage moth, cabbage white butterfly, green looper, lightbrown apple moth, pear looper, vine moth, soybean looper and tobacco looper.

This biological control is a bacterial stomach poison for all caterpillars, which is mixed with water and sprayed onto foliage.

It must be ingested by the actively feeding caterpillar, which dies 3-5 days later.

It is totally safe to beneficial insects, bees, and mammals. Bt is broken down by sunlight within a few days, so repeated applications may be necessary.

H

 

I

J

K

L

Light Brown Apple Moth

N

O

P

Powdery Mildew
Q

R

S

Snails & Slugs

Scab (Potato)

T

U

V

W

Whitefly identification and control ( Green Harvest)

 

Y

Z

 

This page was last updated on 22/12/2012