Should you spray organic fungicide in autumn?

A peach bud in spring with copper spray
A peach bud in spring with copper spray

A lot of people don’t think “organic” and “spray” go together, but actually there’s a couple of relatively ‘safe’ sprays that certified organic growers can use, under strict organic standards.

The only sprays we use are organic fungicides — a little bit of copper, and elemental sulphur — because in a wet season they can make a huge difference in preventing some particularly nasty fungal diseases if you use them in spring.

An apricot with brown rot
An apricot with brown rot

Some people also recommend spraying fungicides on fruit trees after the crop has been picked in autumn, to clean up any residual disease, but this is a bit more controversial.

So, when is the right time to spray? Do your fruit trees really need an autumn fungicide?

The answer is … sometimes!

In our short course Keep Your Fruit Trees Free From Disease we detail those diseases that can benefit from an autumn spray of an organic fungicide, under certain conditions, like brown rot.

So we certainly don’t rule it out, and it can be a useful part of an overall strategy for cleaning up some diseases. However, in most reasonably healthy trees, you don’t need to routinely use a fungicide.

And that’s a good thing, because even organically allowable sprays can have an impact on the environment, particularly the soil, and you should only ever use the minimum amount necessary, and strive instead for a really rich biodiverse garden where natural immunity will be at its highest. (And you should never use chemical fungicides.)

If you’ve had a dry season – as we have in central Victoria this year – there’s been very little fungal disease.

Remove this diseased wood when pruning for good disease control
Remove this diseased wood when pruning, for good disease control

Under these conditions our strategy includes pruning any diseased wood out of the tree, and totally removing it from the tree and the orchard floor, but we won’t be needing to put on a spray at all. Excellent!

Is rain good for fruit?

A lemon covered in raindrops
A lemon covered in raindrops

As a fruit grower, lying in bed listening to rain on the roof can bring up a wide range of emotions, both good and bad. In our typical dry summers most people welcome rain when it comes, so it never seems appropriate for us to express concern about the damage it can do to fruit. However, it hasn’t rained for a while, so this week we reflect on the question – “Is rain good for fruit?”

Like everything in farming, the answer is complicated, and depends on lots of different variables, so let’s break it down a bit.

1. Trees like rain better than irrigation waterup to a point! As a gardener, you’ve probably noticed how “perky” your garden looks just after rain. One of the reasons (apart from the leaves being cleaner) is because the rain carries dissolved nitrogen which is easily absorbed by the plants, giving them a nutritional boost. Too much rain, however, and the soil can become waterlogged, creating anaerobic conditions, which actually stops the plants’ roots being able to take up nitrogen! The other advantages of trees receiving their water from rainfall (rather than irrigation) are that the entire root system gets water (rather than just at the point of water delivery), and if you’ve been keeping your garden on rations due to dry conditions, they just love the opportunity to get their fill of water for a change!

A fungal disease outbreak on an apricot
A fungal disease outbreak on an apricot

2. Rain can trigger fungal disease. One of the biggest pest and disease risks in an organic farm (or garden) is fungal disease, and nearly all fungal diseases are triggered by wet conditions (at the right temperature). In general terms, the more rain, the more fungal disease. This risk is highest at the beginning of the season (i.e., at flowering time in spring), and then gradually decreases as the season progresses. During autumn, if the summer has been generally dry and there is not much fungal disease around, the risk of a new fungal outbreak is relatively low.

Cherries that have cracked in the rain
Cherries that have cracked in the rain

3. Rain can cause physical damage to fruit. This is very specific to the type (and even variety) of fruit. For example cherries are particularly vulnerable to splitting from the rain, and some varieties of apricots also split easily. Hardier fruit like apples and pears, however, rarely experience physical damage from rain.

An apricot with a severe crack caused by rain
An apricot with a severe crack caused by rain

4. “Hard” rain can damage all fruit. Storms that bring rain often also bring hail, and that can be completely devastating to all fruit. Hailstorms are very random and localised, so it”s pretty much the luck of the draw with this one, though if you live in a hail-prone area, netting can definitely be your saviour. All fruit are vulnerable to hail damage, including apples, pears, plums and quinces.

5. Rain is good for the landscape. When you’re trying to grow food in an arid landscape (as we are), the general impact of rain (as long as there’s not too much, or too quickly) is generally FABULOUS! It fills water storages, keeps the bush alive, helps to sustain our farming communities, and helps backyard fruit growers maintain their own food security. We love it….except…. when there’s too much! If rain becomes flooding and the soil becomes saturated for too long, it can lead to ALL sorts of problems! Anaerobic soil conditions, trees dying, waterborne soil disease, nutrient leaching, dams breaking their banks, and the list goes on. We’ve seen it before when the drought broke in 2010/11.

A rainy morning and green grass
A rainy morning and green grass

6. Rain is good for mental health. It’s a generalisation, of course, but very often rain can be a huge relief to farmers and others in the community, especially if it is relieving the pressures of trying to farm in a dry landscape, though as you can probably see from our list, it totally depends on the amount of rain, and the context!

Poppy lapping up a puddle
Poppy lapping up a puddle

Regardless of the timing of rain within the fruit season, it’s important to make sure your soil can act as a big “water storage tank” when it rains. As well as building really healthy soil (which is good for both water storage and drainage in your soil), techniques like swales and keyline (covered in this short course) can make a huge difference to how well your soil will store rainfall.

Diagnosing leaf curl in summer

The dreaded Leaf curl disease on a peach tree

We want to talk about Leaf curl. It’s a common fungal disease of peach and nectarine trees (if you have leaves curling in other types of trees it’s caused by something else).

It may seem strange to be talking about it so late in summer, as it’s a disease that shows up in spring, but bear with us!

If you noticed the disease in your trees last spring, the trees should have completely recovered by now, and grown lots of healthy new leaves (that should look something like the photo below).

Hugh with a healthy young peach tree

However if you’re not sure whether your trees had the disease, it may still be possible to find out, as you may still have remnant diseased leaves in your trees.

They’ll look something like this:

Remnant dead leaves from Leaf curl infection in peach tree

In fact, this can be one of the dignostic tools you can use to help identify whether you had this disease in your trees, in the ongoing detective work we need to be doing to become awesome fruit growers!

These dead and shrivelled leaves are a powerhouse of fungal spores sitting in the tree, just waiting until conditions are perfect next spring to release the spores, and start the disease cycle all over again.

A fresh Leaf curl infection on a peach tree in spring

It’s been often and hotly debated whether it’s worth removing infected leaves from the tree as they emerge in spring, and the answer seems to be no, it doesn’t help reduce the spread of infection once it’s started.

However, the jury is still out on whether removing the remnant leaves in summer will help prevent re-infection the following spring. As always, we err on the side of caution when it comes to practical, hands-on jobs you can do to help your trees stay healthy.

So…get rid of them! Many of these leaves will probably have fallen off of their own accord and rotted away under the tree, but if there are any still in your trees, remove and dispose of them.  

Hot compost is the perfect disposal method, as the high temps reached will kill off the fungal spores, but the organic matter in the leaves won’t go to waste.

Remember, prevention is much better than cure, and hygiene is one of the best defenses we have against all pests and diseases.

Another strong defence is using allowable organic sprays in spring, but it only works if you get the timing right. We’ve included a complete spray program to help you decide what and when to spray in the short course Better Fruit with Wise Organic Spraying.