Melon Master

Melons are prone to a number of pests, diseases and other problems. This year, for example, my melons are looking very poor, aborting their set fruit and generally bearing badly due to heat, dryness and wide temperature fluctuations. It happens to the best of us but here is a general run down of the most common problems you might come across. Luckily here in Australia we don't get the serious pests of melons that are found in other countries.

Flowers or small fruits turning yellow and dying:

There are a number of reasons for this problem. If your female flowers turn yellow and drop off soon after they open and even when they have 'set'. it is usually because they were not pollinated properly. They may not be getting pollinated if there are few bees or other pollinating insects around, or the weather is too wet or cold for the bees. If this happens you may have to hand pollinate the flowers.

If the flowers die either before they open or the small fruits yellow and die  it is usually either because of hot and dry weather, drastic temperature changes between day and night, or because the plant has set some fruit and decides it doesn't need any more. Later on it will probably set some more flowers. It is normal for up to 75% of female flowers to abort either just before flowering or just after.

 Older leaves dying on the plant:

This is usually caused by powdery mildew but some older leaves will die naturally anyway. With powdery mildew you will find that it affects the older leaves first and then you will see white powdery stuff on the other leaves and the plant will wither and die. Luckily this usually happens towards the end of the season when you have usually got some fruit off the plant. Some varieties are resistant to powdery mildew and it can be exacerbated by wet, humid weather or overhead watering. It starts off as small spots on the underside of leaves and gradually spreads to cover the leaf. A fungicide can slow or sometimes stop the mildew if it is used very early.

Seedlings rot off at the base or die:

This is called 'Damping off' and is caused by a fungus. It is common when soil is kept too warm and moist.

Wilting and dying vines:

There are a number of 'wilt' diseases. They cause a rapid wilting and dying of the vine. It begins at a single leaf then spreads to the entire plant. The only remedy is to remove and destroy the plant then either only plant resistant melon varieties for the next few years or plant another type of plant as the disease stays in the soil for a few years. Wilts gum up the vascular system so water cannot move through the plant. If you cut the plant you may find a sticky, oozing substance. Remember that the fungas can be spread by tools, boots or moving soil so be careful if you find it on your place.

Another cause of wilting and dying vines is heat stress. Some varieties just can't stand a lot of heat, even if you keep them watered. Below is a picture of a vine dying from heat. A vine might recover if they have a couple of weeks of cooler weather.

Leaves curl, become yellow or brownish and deformed:

This problem is usually caused by aphids or other pest insects. You can use an insecticide (either chemical or organic) to control the insects.

Fruits are watery and taste insipid:

Usually caused by watering as the fruit ripens. Stop watering as the first fruits are close to ripening.

Fruits split:

Usually caused by watering, or rain as the fruit ripens. A few melon varieties naturally split if they are allowed to get over-ripe on the vine.

Sunburn:

On sunny, hot days over 32 C. many fruits, especially those over half way grown can be prone to sunburn. Many varieties have this problem but especially those with dark coloured fruits. Sunburn starts off as a light patch but then the fruit goes soft and too damaged to eat. It may or may not still ripen depending on how close it was to picking.

Here is a couple of pictures of sunburn:

 To prevent sunburn the only thing you can do when the day is going to be very hot and sunny is to cover the fruits. I cover mine with pieces of cardboard held in place with wire.: