Manual of Gardening Part 17

Another cla.s.s of diseases are the root-galls. They are of various kinds.

The root-gall of raspberries, crown-gall of peaches, apples, and other trees, is the most popularly recognized of this cla.s.s of troubles (Fig.

216). It has long been known as a disease of nursery stock. Many states have laws against the sale of trees showing this disease. Its cause was unknown, until in 1907 Smith and Townsend, of the Bureau of Plant Industry, United States Department of Agriculture, undertook an investigation. They proved that it is a bacterial disease (caused by _Bacterium tumefaciens_); but just how the bacteria gain entrance to the root is not known. The same bacterium may cause galls on the stems of other plants, as, for example, on certain of the daisies. The "hairy-root" of apples, and certain galls that often appear on the limbs of large apple-trees, are also known to be caused by this same bacterium. The disease seems to be most serious and destructive on the raspberry, particularly the Cuthbert variety. The best thing to be done when the raspberry patch becomes infested is to root out the plants and destroy them, planting a new patch with clean stock on land that has not grown berries for some time. Notwithstanding the laws that have been made against the distribution of root-gall from nurseries, the evidence seems to show that it is not a serious disease of apples or peaches, at least not in the northeastern United States. It is not determined how far it may injure such trees.

[Ill.u.s.tration: Fig. 215. The slender tufted growth indicating peach yellows. The cause of this disease is undetermined.]

[Ill.u.s.tration: Fig. 216. Gall on a raspberry root.]

Of obvious insect injuries, there are two general types,--those wrought by insects that bite or chew their food, as the ordinary beetles and worms, and those wrought by insects that puncture the surface of the plant and derive their food by sucking the juices, as scale-insects and plant-lice. The canker-worm (Fig. 217) is a notable example of the former cla.s.s; and many of these insects may be dispatched by the application of poison to the parts that they eat. It is apparent, however, that insects which suck the juice of the plant are not poisoned by any liquid that may be applied to the surface. They may be killed by various materials that act upon them externally, as the soap washes, miscible oils, kerosene emulsions, lime-and-sulfur sprays, and the like.

[Ill.u.s.tration: Fig. 217. Canker-worm.]

There has been much activity in recent years in the identification and study of insects, fungi, and microorganisms that injure plants; and great numbers of bulletins and monographs have been published; and yet the gardener who has tried a.s.siduously to follow these investigations is likely to go to his garden any morning and find troubles that he cannot identify and which perhaps even an investigator himself might not understand. It is important, therefore, that the gardener inform himself not only on particular kinds of insects and diseases, but that he develop a resourcefulness of his own. He should be able to do something, even if he does not know a complete remedy or specific. Some of the procedure, preventive and remedial, that needs always to be considered, is as follows:--

Keep the place clean, and free from infection. Next to keeping the plants vigorous and strong, this is the first and best means of averting trouble from insects and fungi. Rubbish and all places in which the insects can hibernate and the fungi can propagate should be done away with. All fallen leaves from plants that have been attacked by fungi should be raked up and burned, and in the fall all diseased wood should be cut out and destroyed. It is important that diseased plants are not thrown on the manure heap, to be distributed through the garden the following season.

Practice a rotation or alternation of crops (p. 114). Some of the diseases remain in the soil and attack the plant year after year.

Whenever any crop shows signs of root disease, or soil disease, it is particularly important that another crop be grown on the place.

[Ill.u.s.tration: Fig. 218. A garden hand syringe.]

See that the disease or insect is not bred on weeds or other plants that are botanically related to the crop you grow. If the wild mallow, or plant known to children as "cheeses" _(Malva rotundifolia_), is destroyed, there will be much less difficulty with hollyhock rust. Do not let the cabbage club-root disease breed on wild turnips and other mustards, or black-knot on plum sprouts and wild cherries, or tent-caterpillars on wild cherries and other trees.

[Ill.u.s.tration: Fig. 219. A knapsack pump.]

Always be ready to resort to hand-picking. We have grown so accustomed to killing insects by other means that we have almost forgotten that hand-picking is often the surest and sometimes even the most expeditious means of checking an invasion in a home garden. Many insects can be jarred off early in the morning. Egg-ma.s.ses on leaves and stems may be removed. Cutworms may be dug out. Diseased leaves may be picked off and burned; this will do much to combat the hollyhock rust, aster rust, and other infections.

[Ill.u.s.tration: Fig. 220 A compressed-air hand pump for garden work.]

[Ill.u.s.tration: Fig. 221 A bucket pump.]

[Ill.u.s.tration: Fig. 222 A bucket pump.]

[Ill.u.s.tration: Fig. 223 A cart-mounted pump.]

Keep close watch on the plants, and be prepared to strike quickly. It should be a matter of pride to a gardener to have in his workhouse a supply of the common insecticides and fungicides (Paris green or a.r.s.enate of lead, some of the tobacco preparations, white h.e.l.lebore, whale-oil soap, bordeaux mixture, flowers of sulfur, carbonate of Copper for solution in ammonia), and also a good hand syringe (Fig. 218), a knapsack pump (Figs. 219, 220), a bucket pump (Figs. 221, 222), a hand bellows or powder gun, perhaps a barrow outfit (Figs. 223, 224, 225), and if the plantation is large enough, some kind of a force pump (Figs.

226, 227, 228). If one is always ready, there is little danger from any insect or disease that is controllable by spraying.

[Ill.u.s.tration: Fig. 224. A garden outfit.]

[Ill.u.s.tration: Fig. 225. A cart-mounted barrel pump.]

[Ill.u.s.tration: Fig. 226. A barrel hand pump.]

[Ill.u.s.tration: Fig. 227. A barrel outfit, showing nozzles on extension rods for trees.]

_Screens and covers._

There are various ways of keeping insects away from plants. One of the best is to cover the plants with fine mosquito-netting or to grow them in hand-frames, or to use a wire-covered box like that shown in Fig.

229. In growing plants under such covers, care must be taken that the plants are not kept too close or confined; and in cases in which the insects hibernate in the soil, these boxes, by keeping the soil warm, may cause the insects to hatch all the sooner. In most cases, however, these covers are very efficient, especially for keeping the striped bugs off young plants of melons and cuc.u.mbers.

[Ill.u.s.tration: Fig. 228. A truck-mounted barrel hand spray Pump.]

Cut-worms may be kept away from plants by placing sheets of tin or of heavy glazed paper about the stem of the plant, as shown in Fig. 230.

Climbing cut-worms are kept off young trees by the means shown in Fig.

231. Or a roll of cotton may be placed about the trunk of the tree, a string being tied on the lower edge of the roll and the upper edge of the cotton turned down like the top of a boot; the insects cannot crawl over this obstruction (p. 203).

[Ill.u.s.tration: Fig. 229. Wire-covered box for protecting plants from insects.]

[Ill.u.s.tration: Fig. 230 Protecting from cut-worms.]

The maggots that attack the roots of cabbages and cauliflowers may be kept from the plant by pieces of tarred paper, which are placed close about the stem upon the surface of the ground. Fig. 232 ill.u.s.trates a hexagon of paper, and also shows a tool used for cutting it. This means of preventing the attacks of the cabbage maggot is described in detail by the late Professor Goff (for another method of controlling cabbage maggot see p. 201):--

[Ill.u.s.tration: Fig. 231 Protecting trees from cut-worms.]

[Ill.u.s.tration: Fig. 232 Showing how paper is cut for protecting cabbages from maggots. The Goff device.]

"The cards are cut in a hexagonal form, in order better to economize the material, and a thinner grade of tarred paper than the ordinary roofing felt is used, as it is not only cheaper, but being more flexible, the cards made from it are more readily placed about the plant without being torn. The blade of the tool, which should be made by an expert blacksmith, is formed from a band of steel, bent in the form of a half hexagon, and then taking an acute angle, reaches nearly to the center, as shown in Fig. 232. The part making the star-shaped cut is formed from a separate piece of steel, so attached to the handle as to make a close joint with the blade. The latter is beveled from the outside all round, so that by removing the part making the star-shaped cut, the edge may be ground on a grindstone. It is important that the angles in the blade be made perfect, and that its outline represents an exact half hexagon. To use the tool, place the tarred paper on the end of a section of a log or piece of timber and first cut the lower edge into notches, as indicated at _a,_ Fig. 232, using only one angle of the tool. Then commence at the left side and place the blade as indicated by the dotted lines, and strike at the end of the handle with a light mallet, and a complete card is made. Continue in this manner across the paper. The first cut of every alternate course will make an imperfect card, and the last cut in any course may be imperfect, but the other cuts will make perfect cards if the tool is correctly made, and properly used. The cards should be placed about the plants at the time of transplanting. To place the card, bend it slightly to open the slit, then slip it on to the center, the stem entering the slit, after which spread the card out flat, and press the points formed by the star-shaped cut snugly around the stem."

_Fumigating._

An effective means of destroying insects in gla.s.s houses is by fumigating with various kinds of smoke or vapors. The best material to use for general purposes is some form of tobacco or tobacco compounds.

The old method of fumigating with tobacco is to burn slowly slightly dampened tobacco stems in a kettle or scuttle, allowing the house to be filled with the pungent smoke. Lately, however, fluid extracts and other preparations of tobacco have been brought into use, and these are so effective that the tobacco-stem method is becoming obsolete. The use of hydrocyanic acid gas in greenhouses is now coming to be common, for plant-lice, white-fly, and other insects. It is also used to fumigate nursery stock for San Jose scale, and mills and dwellings for such pests and vermin as become established in them. The following directions are from Cornell Bulletin 252 (from which the formulas in the succeeding pages, and most of the advice, are also taken):--

"No general formula can be given for fumigating the different kinds of plants grown in greenhouses, as the species and varieties differ greatly in their ability to withstand the effects of the gas. Ferns and roses are very susceptible to injury, and fumigation if attempted at all should be performed with great caution. Fumigation will not kill insect eggs and thus must be repeated when the new brood appears. Fumigate only at night when there is no wind. Have the house as dry as possible and the temperature as near 60 as practicable.

"Hydrocyanic acid gas is a deadly poison, and the greatest care is required in its use. Always use 98 to 100 per cent pure pota.s.sium cyanide and a good grade of commercial sulfuric acid. The chemicals are always combined in the following proportion: Pota.s.sium cyanide, 1 oz.; sulfuric acid, 2 fluid oz.; water, 4 fluid oz. Always use an earthen dish, _pour in the water first,_ and add the sulfuric acid to it. Put the required amount of cyanide in a thin paper bag and when all is ready, drop it into the liquid and leave the room immediately. For mills and dwellings, use 1 oz. of cyanide for every 100 cu. ft. of s.p.a.ce. Make the doors and windows as tight as possible by pasting strips of paper over the cracks. Remove the silverware and food, and if bra.s.s and nickel work cannot be removed, cover with vaseline. Place the proper amount of the acid and water for every room in 2-gal. jars. Use two or more in large rooms or halls. Weigh out the pota.s.sium cyanide in paper bags, and place them near the jars. When all is ready, drop the cyanide into the jars, beginning on the top floors, since the fumes are lighter than air.

In large buildings, it is frequently necessary to suspend the bags of cyanide over the jars by cords running through screw eyes and all leading to a place near the door. By cutting all the cords at once the cyanide will be lowered into the jars and the operator may escape without injury. Let the fumigation continue all night, locking all outside doors and placing danger signs on the house."

In greenhouses, the white-fly on cuc.u.mbers and tomatoes may be killed by overnight fumigation with 1 oz. of pota.s.sium cyanide to every 1000 cu.

ft. of s.p.a.ce; or with a kerosene emulsion spray or whale-oil soap, on plants not injured by these materials.

The green aphis is dispatched in houses by fumigation with any of the tobacco preparations; on violets, by fumigation with 1/2 to 3/4 oz.

pota.s.sium cyanide for every 1000 cu. ft. of s.p.a.ce, leaving the gas in from 1/2 to 1 hr.

The black aphis is more difficult to kill than the green aphis, but may be controlled by the same methods thoroughly used.

_Soaking tubers and seeds._

Potato scab may be prevented, so far as planting infected "seed" is concerned, by soaking the seed tubers for half an hour in 30 gal. of water containing 1 pt. of commercial (about 40 per cent) formalin. Oats and wheat, when attacked by certain kinds of s.m.u.t, may be rendered safe to sow by soaking for ten minutes in a similar solution. It is probable that some other tubers and seeds can be similarly treated with good results.

Potatoes may also be soaked (for scab) one and one-half hours in a solution of corrosive sublimate, 1 oz. to 7 gal. of water.

_Spraying._

The most effective means of destroying insects and fungi however, in any general or large way, is by the use of various sprays. The two general types of insecticides have already been mentioned--those that kill by poisoning, and those that kill by destroying the body of the insect. Of the former, there are three materials in common use--Paris green, a.r.s.enate of lead, and h.e.l.lebore. Of the latter, the most usual at present are kerosene emulsion, miscible oils, and the lime-sulfur wash.

Sprays for fungi usually depend for their efficiency on some form of copper or sulfur, or both. For surface mildews, as grape mildew, dusting flowers of sulfur on the foliage is a protection. In most cases, however, it is necessary to apply materials in liquid form, because they can be more thoroughly and economically distributed, and they adhere to the foliage better. The best general fungicide is the bordeaux mixture.

It is generally, however, not advisable to use the bordeaux mixture on ornamental plants, because it discolors the foliage and makes the plants look very untidy. In such cases it is best to use the ammoniacal copper solution, which leaves no stain.