Gareth Carter: Hot summer causes explosion in insect numbers

After a hot summer there has been an explosion in insect numbers including whitefly, aphids, mites, scale and thrip on many plants.

GARDENING

The past week has had a number of cool mornings with a distinctly autumn feel about them.

The cool start has for the most part given way to glorious warm hot days.

A couple of plants that I associate with autumn are the Chilean guava and the feijoa.

I have an exceptionally early variety of feijoa growing at home and the first ripe fruit have fallen this week.

The fruit of the Chilean guava are just starting to get towards harvest size and give off their delicious perfume.

My youngest son adores this fruit and gained a good snack from Grandma's Chilean guava plant during the last weekend.

The name Chilean guava is the common name for the bush given that the plant originates from Chile where its fruits are grown commercially, exported to Japan and sold locally.

The other common name "NZ cranberry" is often a source of confusion, as other than the look of the fruit, the plant growth and fruit taste are nothing similar to the "real" cranberry.

The Chilean guava produces attractive white flowers during spring and then forms round red berries (about 0.5-1.5cm across) during the summer months.

Towards late February and during March these berries reach maturity.

It is the ripening berries that produce the delicious smell. They are also delicious to eat fresh as well as being suitable for making juices, jams and other preserves.

The plants yield quite well with a 3-year-old plant producing about 1kg of fruit which will increase by about 1kg a year subsequently.

The plants themselves have a number of landscaping uses.

If left unchecked they will grow to 1.5m x 1m. They are best trimmed each year after fruiting to maintain some form, otherwise they can become a rather straggly and leggy bush.

They are great grown in a courtyard situation where the scent when fruiting coincides with barbecue season.

The plants can be kept trimmed to size as the space available allows, by pruning after fruiting each year.

They are suitable for containers and patio situations where their drought-hardy tendencies can be useful, though lack of water can affect fruit quality.

The fruit of the Chilean guava are just starting to get towards harvest size and give off their delicious perfume.

The Chilean guava is regularly grown as a topiary.

Its dense-forming habit and small leaves make it an ideal candidate as a successful topiary which offers not just good form but the added value of scent and fruit.

They also make a marvellous fruiting hedge.

Their leaves resemble those of buxus, though slightly more rounded, and their dense-growing habit right from the base of the plant makes the Chilean guava a great hedge to consider.

The growth habit is much faster than buxus, allowing establishment of a 30cm-high hedge in about two years or less rather than three to four years.

The trade-off of a faster growing hedge is that it will need trimming two to three times a year to maintain a tidy look.

Culturally they are an easy care plant. The main insect offender to be aware of is thrips. These will often attack plants that become stressed from drought, but are easily controlled with an insecticide such as Yates Mavrik if it becomes a problem.

They are hardy to around -6C and are happy growing in full sun or part shade.

They are tolerant of salty air but perform far better if they are out of the prevailing wind in a slightly more sheltered situation. They grow best in fertile well-drained soil; however, being very versatile they will also grow well in clay and even in sandy soils.

Pest watch

After a hot summer there has been an explosion in insect numbers including whitefly, aphids, mites, scale and thrip on many plants.

The rain a week ago created more humidity which is now showing up many cases of blight, mildew and other fungus infections.

What to look for now: Maintain vigilant monitoring on crops for whitefly and caterpillar damage on tomatoes and cucurbits – it is wise to spray at first sign to keep the population down for as long as possible. (Population can build rapidly and once in large numbers control is significantly more difficult).

Mavrik is a good control – concentrate on the new growth where the pest is worst.

Spraying with Grosafe Freeflo Copper mixed with Enspray 99 is recommended to control powdery and downy mildew on cucurbits and to protect tomatoes from blight.

Another prevalent pest at this time of year is passion vine hopper, which attacks a wide range of plants. Insect sprays Mavrik and Pyrethrum will control this.

Citrus

It has been a good season for growth and fruit development on citrus but be wary, I have recently seen a lot of citrus covered in sooty mould and closer inspection shows the cause – a heavy infestation of scale on the undersides of leaves.

Now is the time to apply a spray of Yates Mavrik combined with 10ml per litre of Grosafe Enspray 99 to kill the invaders and protect the new season growth which will ensure good fruit production.

A follow-up spray later in March would be advisable.

Now is also a good time to fertilise citrus and ensure they are being watered deeply.

The plants will have fruit formed on them now and if they become stressed due to drought, fruit may drop or quality can deteriorate.

If your citrus are growing in pots or containers then ensure you use a specialist citrus fertiliser that is suitable, such as Burnets Gold Citrus Fertiliser.

If leaves are showing signs of yellowing then a liquid fertiliser feed of Yates Thrive Citrus Liquid Plant Food is highly recommended and will give quick results to green the leaves up.

Remember, a well fed, well watered healthy tree will be far less prone and more resilient to insect and disease attacks.

The addition of Saturaid re-wetting granules to citrus growing in containers is highly recommended. This product should be applied annually - it channels water to the root zone where it is needed most.

It promotes even water distribution so there is less water run-off and dry spots in potting mix and soils. It makes watering, rainfall and fertiliser more effective. It can also be used in the garden, even in sandy, clay or compacted soils.

Have a good week.

• Gareth Carter is general manager of Springvale Garden Centre.