The Practical Planter

Banana pests and their control

From "Banana Production in the South Pacific" Commission handbook edited by MICHEL LAMBERT.

Banana beetle borer. This is the most serious insect pest of bananas in the South Pacific. It also ccurs in Central and South America, in Africa, Madagascar, Southern India, Indonesia Taiwan nd Australia. It has other common names such as the banana borer and banana weevil, but the :ientific name is Cosmopolites sordidus Germ.

The full-grown adult is a true r eevil about half an inch long with long snout. It changes colour from ;ddish-brown to black as it gets Ider and has a hard shell. When ;moved from the moist tissue of le banana plant, it dries out to a rey colour.

The adult female lays its pure rhite eggs in cavities in the corm ist about ground-level during the ight. The weevils feed at night too, nd hide during the daytime. The ggs hatch in about eight days and ie young grubs which are creamy dike in colour, legless and with a ody that is distinctly curved and wollen in the middle, and measuring bout half an inch long when latured, immediately start to bore awards, making tunnels as they go.

These tunnels get bigger as the rubs mature and often have a iameter of half an inch. The grubs tore through the corm towards the lutside as they mature and finally lupate just below the surface.

It’s about eight days before the idult emerges.

How it spreads

Injury to the banana corm is ;aused by the grub as it feeds and unnels through the tissue. The corm tecomes riddled with tunnels which lecay and turn it into a mass of otted material. This kind of injury >revents nourishment moving into the ilant and the leaves wither and die. rleavily infested plants can easily be lushed over and bunches of fruit become small.

The spread of beetle borer takes slace in two main ways; in infested planting material being moved from me place to another, or by crawling into adjacent areas. The first mentioned means of spread is by far the most important and the second would only occur after the introduc

tion of infested material in the first pj ace> There is no authentic evidence to support the suggestion that adult weevils move by flight, even though they have fully developed wings.

It may not be easy to detect light infestations, and backward plants or those showing premature withering of leaves, should be examined by slicing the corm with a knife or machete and thoroughly searching for tunnels or grubs. Traps may be prepared in the plantation using the corm of a freshly harvested plant; the stem is cut off about a foot above ground leaving the corm which is split parallel to the ground at ground level. It is then lifted and propped open about one inch with a stone or stick. Adult beetles will seek the shelter of this cavity and may be collected and destroyed.

Control : Prevention of introduction of the pest to beetle-free areas:— • Vigorous plants should be obtained from plantations free of beetle-borer, and be removed from the plantation soon after digging.

O Examine all planting material very carefully and discard suspect la £ ts 3 • Pare corms by removing a thin slice of surface tissue. • Dip plants prepared as above in either 0.1 per cent. Dieldrin or 0.2 per cent. Aldrin.

• Plant the treated material as soon as possible. © Do not replant old areas until all remaining plants and corms have been removed.

Control measures using insecticides ? irec^i.?i a i5 st n H?® ®«“iV WeeVll Stage m established plantations. ,

Properly prepared

. , , , Plantations should be properly pr pared for application of insecticides by removing dead leaves and trash fr° m ar o un(l t b. e base of plants, Regular desuckenng and removal of old plant material will greatly assist in the control of the pest. Spray ap plications should be made at the rate of one pint per plant ot: 0.05 per cent, active ingredient Dieldnn, or . CCnt ‘ actn,e mgredient Aldrm, or .. . 0.1 per cent. active ingredient Heptachlor. . Misting machine applications may be used to apply Dieldnn at the rate eight gallons per acre of a dilution oj 10 fluid ounces of 15 per cent, Dieldnn per two gallons of water.

The motor of the machine should be run at low revolutions to be effective.

These sprays should be applied thoroughly to the bases of plants including the suckers and to 12

The adult banana beetle borer, four times its actual size.

Note the beetle, life size at the bottom of the picture.

void contact with these materials

dies of soil around the plants, in » periods of greatest adult activity, lis usually occurs in the spring and tumn months and sprays should applied in the September to yvember period and again between arch and May in the first year, lereafter an application during each ring is necessary and this may be luced to once every two years after 0 or three successive applications infestations have been reduced to low level.

When using Dieldrin, Aldrin or sptachlor, care must be taken to oid contact of these materials with t skin and the precautions printed 1 the container should be read care lly and strictly observed.

A serious pest

Banana scab moth: This is a rious pest in the islands of the mth-West Pacific and also occurs tropical North Queensland and the alay Archipelaga—it’s not found in e Cook Islands or in Hawaii. It’s mmonly called scab moth but its ientific name is Nacoleia octasema deyr.).

Both wild and cultivated bananas e attacked by this pest as well as Manila hemp, pandanus, nipa palm, diconia and maize, all of which ay provide an alternate host.

The adult has a wing span of )out three-quarters of an inch and buff coloured with two dark brown arks in each wing. It is rarely seen the daytime except when disturbed om the shelter of the plant.

The female scab moth lays its fle greenish-white eggs in clusters i the flag leaf or in that area just ■ior to the emergence of the bunch, hatching occurs in about four days id the small transparent yellow floured caterpillars crawl under the nopened bracts of the emerging imch and commence feeding.

As the caterpillar grows it changes flour to a pale pinkish shade and iaracteristic spots appear on its ody close to the head. In the course E feeding the pest causes the typical :abby appearance of the fruit and eposits masses of dark frass between le fingers and hands on the bunch, /hen fully fed after about 14 days le caterpillar enters its pupal stage i a drop-shaped case among the ry rubbish.

After about eight days the adult 10th emerges and the life cycle is ompleted in about 28 days.

Injury is caused to the banana ruits by the caterpillars which feed n the skin and this damage results

in the typical dry, scabby appear ance of the fruit on the maturing bunches.

Scab moth damaged fruit is not acceptable for export and its main use is for local consumption, hence it is very important to control the pest. This is best attempted at the stage when the caterpillars first enter the bunch.

Control : The application of in secticides just before the bunch emerges has been the most successful method yet devised. Attempts to introduce a parasite which would attack this pest have not been success ful so far, but the thorough and timely application of insecticides will reduce damage very considerably.

Successful control depends on strictly carrying out the following operations:— • Apply a 2 per cent. DDT dust at the rate of 1 lb per 50 to 100 bunches, depending on size. • The first application of insec ticide should be timed to be made to the bunch as the flag leaf emerges. • Lifting of the bracts and blow ing the insecticide dust into each hand of developing fruit. • Repeat treatment weekly until the fingers of bananas are well separated.

Anew method of applying DDT to emerging bunches has been developed recently in Western Samoa.

This consists of a long rod with a hooked outlet to which an injector type nozzle is fitted which is used to penetrate the “cob” or emerging bunch, and through which is applied an injection of DDT emulsion.

The advantages of this method are that it can be applied from the ground and is much quicker than dusting.

Nematodes (eelworm) : Several types of nematodes have been found attacking banana plants, and these are mainly found on the roots. The most serious one is a burrowing kind known as Radopholus similis whose larvae or eelworms burrow into the roots where they feed and multiply in large numbers.

Tiny holes

The tiny holes left by the burrow ing activity of the nematodes allow fungi which normally live in the soil to enter and cause the rcKfls to rot.

This nematode only lives on a few kinds of plants of which the banana and sugarcane are two of the most important, and does not survive in the soil by itself for very long.

Infestations are easily identified by examination of the roots. Those which have been attacked will show small hollows or sunken areas, which are often dark in colour and when scraped or cut show reddish brown coloured areas near the surface.

Infested plants often appear in patches and do not respond to fertilisers, irrigation or other atten tion.

To control this nematode it is important to:— • Select healthy plants for plant ing. • Plant in nematode free soils — that is in soil in which bananas have not been grown before or which has been completely free of banana plants for at least one year. • Treat planting material, by completely immersing in hot water after cleaning them of all roots and soil at a temperature of 128 deg.

Fahr. for a period of 20 minutes after which the plants should be allowed to cool and be planted without delay.

Another way is by severely paring off all roots and a layer of outside corm followed by dipping in a mixture of 2i pints DBCP (nemagon 90 (R >) to 100 gallons of water prior to planting.

The root knot nematode (Meloido gyne incognita) is common to bananas and many other plants. It causes swellings to appear on plant roots which may be quite large and form in bunches.

In warm soils a long period of activity may be expected, but this rarely results in the killing of plant tissue, and in the case of large plants like bananas, growth is not affected to any extent. This nematode is not considered to be serious enough to warrant the application of control measures.

Banana aphid ; This insect is

phids spread the virus

portant because it is the carrier of 3 virus causing bunchy top in nanas and related species of plants. itself it does little damage, but bids having fed on bunchy top :ected plants are quite capable of jvement to healthy plants to which ; virus is readily transmitted when ;ding commences.

Its most common name is the nana aphid, but it is sometimes lied the bunchy top aphid, and is own by the scientific name of ntalonia nigronervosa.

The adult aphid is a small dark own insect about the size of a i head, which usually has no wings. the spring months of July to ptember however, some of the

insects have wings and move by this means from plant to plant.

It is not economical to apply insecticides to the whole plantation but it is of utmost importance to kill all aphids on bunchy top infected plants, and on the plants which surround them.

A cheap and effective method of killing the insects on bunchy top plants is to spray thoroughly with power kerosene. This also assists in the destruction of the plants. In treat ment of infested healthy plants, insecticides such as Metasystox< R ) at 0.02 per cent, or Rogor( R ) at 0.02 per cent, may be used.

These insecticidal treatments are very useful if the establishment of virus-free banana plant nurseries is being attempted.

Other pests

Other pests : Several other pests attack bananas at times but their actively is rarely serious enough to warrant the application of insec ticides for their control.

The case moth or bagmoth may be troublesome on bananas which are interplanted among cocoa which is one of the main host plants for this pest. The caterpillars live within a case of dead leaf pieces which they make from the plants on which they are feeding. Good control is obtained using sprays of DDT at 0.1 per cent, or Carbaryl (Seven < R )) at 0.1 per cent., repeated after two or three weeks if necessary.

Growers should be on the alert for other pests as some, such as banana rust, thrips and red spider, which are present in Australia do not occur in the Pacific Islands. The discovery of any unusual insect or condition suspected of being the result of insect activity should be brought to the attention of an authority for identification.

Hereunder are listed the safe hold ing periods for fruit after it has been treated with insecticides most likely to be used on bananas.

BHC, Lindane; not recommended between flowering and picking because of possible tainting. Carbaryl, three days. DDT, four weeks.

Demeton-S-methyl, three weeks.

Dieldrin, must not be applied to fruit at any time. Dimethoate, one week.

Endrin, must not be applied to fruit at any time. Fenthion, two weeks.

Maldison, one week (safe after three days but may cause off-flavour if interval less than seven days).

Mevinphos, three days. Tetradifon, three days.