Part 8

Date of Total Small Large Wormy Bagging Nuts Chestnut Chestnut Nuts Nuts Bagged Weevil Weevil Year and Orchard Number Number Number Percent 1945 July 9 52 2 5 13 Glenn Dale, Md. Aug. 1 46 4 2 13 Aug. 15 107 18 11 27 Fairfax, Va. Aug. 21 110 22 13 32 Sept. 12 123 63 11 60 1946 July 12 65 0 0 Glenn Dale, Md. July 18 40 0 0 July 26 67 0 0 Aug. 1 71 0 0 Aug. 9 29 1 0 3 Aug. 14 88 3 2 6 Aug. 23 53 18 2 38 Aug. 29 53 23 11 64 Fairfax, Va. July 26 98 0 0 0 Aug. 15 168 0 0 0 Sept. 4 164 139 16 95 1947 Aug. 15 54 5 1 11 Glenn Dale, Md. Aug. 25 38 8 0 21 Sept. 2 24 7 1 33 Sept. 9 42 18 4 52 Sept. 15 56 29 7 64 Sept. 22 90 27 11 64 Sept. 29 143 83 22 73 Fairfax, Va. Aug. 26 35 9 1 29 Sept. 10 58 25 4 50 Sept. 28 50 35 7 84 Oct. 7 217 177 22 92 Elkton, Md. Aug. 21 139 11 13 17 Sept. 4 83 22 25 57 Sept. 18 116 21 35 48 Oct. 1 108 31 44 69

+Spray Experiments in 1944+

Shortly after adults of the large chestnut weevil first appeared in the orchards in 1944, six trees isolated from other chestnuts were selected for treatment. Five trees were sprayed with from 1 to 5 pounds of technical DDT plus 1/2 pound of sodium lauryl sulfate to 100 gallons of water, and the sixth tree was left untreated as a check. A thorough application of a coarse, drenching spray at a pressure of 400 pounds per square inch was used in an attempt to force the DDT between the many spines of the burs. The DDT used was very coarse, and difficulty was experienced in getting a proper suspension. This formula was used, however, in preference to one which contained other ingredients that might have formed a protective coating over the particles of DDT. Heavy rains prevented later spray applications.

Adult weevils obtained by jarring untreated trees were then confined in screen cages placed over the lower branches of the trees. At the end of each cage was a cloth sleeve which was tied to the limb to hold the cage in place. The treatments used and the results are given in Table 2.

Table 2. Percentage mortality of chestnut weevils placed in field cages on trees at different intervals after they had been sprayed with with DDT, 1944.

Strength of DDT (lb. per Small Chestnut Weevil Large Chestnut Weevil 100 gal.) 48 Hrs. 96 Hrs. 144 Hrs. 48 Hrs. 96 Hrs. 144 Hrs.

1 0 61 100 25 50 100 2 19 69 100 0 34 100 3 4 50 100 0 40 100 4 27 87 100 0 50 100 5 18 50 100 30 46 100 Check 0 0 0 0 7 7

Although the results obtained the first few days in the cages containing treated foliage were somewhat irregular, because of the small numbers of tests made, all weevils were killed within 6 days. The results indicate definitely that DDT is toxic to the adults of both species of weevils. No consistent differences between species were noted.

As the matured nuts dropped from the treated trees, daily collections were made, and one-third of each collection was used as a sample in determining the percentage of wormy nuts. At the time the nuts drop, the holes in the shell through which the eggs were inserted are very difficult to detect. The nuts were therefore held in wire baskets to permit most of the larvae to emerge before the final examination. All nuts not showing exit holes were cut open to find out whether they were wormy. The marked increase in clean nuts after all treatments indicates that DDT is a promising insecticide for use against the weevils. The treatment and infestation records for the sprayed trees and the check tree are given in Table 3, which also includes the results obtained in later years.

+Spray Experiments 1945 to 1947+

Spring frosts in 1945 destroyed 95 per cent of the crop of chestnuts in the Eastern States. Only six trees of different species and ages in the Government orchard at Glenn Dale, had sufficient nuts for experimental purposes. Applications of a 50 per cent DDT wettable powder in the proportions of 4 and 6 pounds plus 1/2 gallon of summer oil as a sticker to 100 gallons of water were made on August 20 and September 9.

Spring frosts again damaged the orchards in 1946, destroying about 80 per cent of the possible chestnut crop, and leaving only eight trees in the Government orchard that were suitable for experimental purposes. The remaining trees having a small scattered crop were disregarded. A mixture consisting of equal parts by weight of DDT and kaolin 41 was used in the strength of 2 pounds of DDT to 100 gallons of water. The time and number of applications were varied.

Table 3. Results of spray tests with DDT against chestnut weevils, 1944-1947.

Larvae Emerging from Sample Reduction Nuts Small Large Wormy of DDT (per Application in Chestnut Chestnut Nuts Injured 100 gal.) Sample Weevil Weevil Nuts Year Pounds Number Number Number Percent Percent

Government Orchard, Glenn Dale, Md.

1944 1 Aug. 14 533 1896 21 44 42 2 646 402 45 25 67 3 712 421 5 18 76 4 951 814 5 22 71 5 1844 850 10 16 79 0 976 3238 100 76 1945 2 Aug. 20 & Sept. 9 660 434 38 30 57 3 305 285 58 22 69 0 297 1164 61 70 1946 2 Aug. 15 & 30, Sept. 11 621 131 12 9 90 2 Aug. 15 & 30 371 171 23 19 79 2 Aug. 30 & Sept. 11 292 87 21 26 71 2 Aug. 15 & Sept. 11 949 553 190 43 53 2 Aug. 30 1267 1407 98 43 53 2 Aug. 15 1212 3207 66 43 53 2 Sept. 11 368 1832 53 58 36 0 870 5364 134 91 1947 2 Aug. 13 & 29, Sept. 12 4084 3817 234 30 66 2 Aug. 13 & 29 2618 4255 151 52 40 2 Sept. 12 3029 9498 402 79 9 2 Aug. 13 2639 5049 198 51 41 0 974 4714 121 87

Van Reynolds Orchard, Elkton, Md.

1947 2 Aug. 21, Sept. 4 & 18 1153 264 64 14 84 2 Sept. 4 & 18 338 5 118 67 23 2 Aug. 21 & Sept. 18 149 18 59 34 61 2 Aug. 21 & Sept. 4 669 102 12 51 41 2 Sept. 18 324 63 129 77 11 2 Sept. 4 270 303 67 56 36 2 Aug. 21 500 192 127 57 34 0 338 152 118 87

Sprays containing DDT were applied in two orchards in 1947, the Government orchard at Glenn Dale, and the Van Reynolds orchard at Elkton, Md. Spring frosts injured 50 per cent of the chestnut crop at Glenn Dale and 70 per cent at Elkton, and as a result only a few trees suitable for tests were available. The remaining trees were not sprayed. Four pounds of the standard mixture of equal parts of DDT and kaolin were used to 100 gallons of water in all applications.

In Table 3 will be found information on the quantities of DDT used, the schedules followed, and the results obtained during the period 1944 through 1947.

These results indicate clearly the effectiveness of DDT in chestnut weevil control, in spite of numerous discrepancies brought about by the small number and variability of the trees available for the tests. As might be expected, programs of three applications were more effective than those of only one or two. Of the single applications, those put on during the latter half of August were much more effective than those made during the first half of September, presumably because most of the eggs had been laid by the early part of September.

These experiments gave fairly exact information on the relative abundance of the two species of weevils. At Glenn Dale the small chestnut weevil constituted 92 to 98 per cent of the population; at Elkton, 61 per cent.

The matured nuts that fell from count trees were collected daily, and one-third of each lot collected was used as a sample for determining the percentage of wormy nuts. It was possible, therefore, to obtain a rough estimate of the numbers of larvae produced on each tree. In 1946, from 1,863 nuts on a tree sprayed three times, 429 larvae emerged; and from a comparable unsprayed tree having 2,610 nuts 16,494 larvae emerged. In 1947, 1,350 larvae were produced on 9 trees with an average crop of 1,361 nuts sprayed three times, compared with 14,505 larvae from 2,922 nuts on an unsprayed tree. These figures indicate that DDT sprays bring about large decreases in the numbers of weevils and that the proper use of DDT sprays on all host trees over a period of a few years would doubtless reduce the infestation to a point where fewer applications would be necessary for effective control of the chestnut weevils.

+Tentative Recommendations+

For the benefit of those who wish to try DDT for chestnut weevil control, the following tentative recommendation is made:

Thoroughly apply +to all parts of the tree+ 2 pounds of DDT in 100 gallons of water. For example, use 4 pounds of a wettable powder that contains 50 per cent of DDT, or 8 pounds of one that contains 25 per cent of DDT. Make three applications, the first about 30 days before the first nut is due to drop, and the second and third after intervals of 12 days. Unless the entire bur, especially that portion near the stem end where most of the feeding punctures are made, +is thoroughly covered+ with a film of DDT, the weevils may feed without being affected by the insecticide. In handling DDT, one should use the same care as with such well-known poisons as lead arsenate, Paris green, calcium arsenate, and nicotine.

* * * * *

Mr. Gravatt: I might say that Mr. Van Leeuwen has used only a small section of our experimental orchard, and right near-by would be large sections not used. The weevils are not killed quickly by the DDT, they are somewhat resistant, and so we think quite a number of weevils come over and deposit eggs before they are killed by this DDT, because they don't lose any time getting to work on the nuts. He hopes to have much better results where the entire orchard is sprayed. This year we sprayed our entire orchard twice, and it is a real pleasure to go out there now and gather up nuts and not be eating weevils when we do eat them.

President Davidson: Well, Mr. Gravatt will now give us a talk on Diseases Affecting the Success of Tree Crop Plantings, and I am sure we all are on our toes to hear about that. Mr. Gravatt.

Mr. Gravatt: I only ask a few minutes to show a few slides.

(Slides shown.)

Diseases Affecting the Success of Tree Crop Plantings

G. F. GRAVATT and DONALD C. STOUT

Division of Forest Pathology, Plant Industry Station, Beltsville, Maryland.

Mass plantings of many trees of the same kind frequently result in an increase in the severity of insect pests and diseases. Leaf diseases, for instance, spread quickly through such plantings when weather conditions favor growth of the causal organisms. Plants on sites unfavorable to a specific tree species also are responsible for disease increases. Chinese chestnuts grown on a site where they are subject to early-fall and late-spring frosts will fail. Not only will crops be reduced by the killing of buds or blooms, but the twigs, or even whole trees, may be killed by freezing. The blight fungus develops rapidly on such injured trees and may mislead people into thinking that the blight fungus is the primary cause of the killing.

Still another factor that determines the damage by diseases, and thus the success or failure of nut tree plantings, is the ignoring of soil and fertilizer requirements. Trees weakened by drought, because they are on a site having a soil too shallow for good root growth, are much more subject to attack even by weakly parasitic fungi than those growing on a site with deeper soil. Innumerable dying twigs and branches with fungi growing on them are sent to the U. S. Department of Agriculture or State experiment stations with requests that the disease be identified, when the real trouble is lack of water for the roots. Weak trees are much more subject to winter injury than vigorous ones.

Trees require a good supply of plant food materials and water to produce profitable crops. Tho heaviest bearing chestnut trees we have observed were grown in an irrigated orchard in California and in a poultry yard in the East where chicken droppings actually formed a mulch under the trees. However, if you wish to kill a young chestnut tree quickly, just apply a very heavy application of chicken manure; the point is that trees must become adjusted to chicken manure by gradual applications.

Another way to damage a tree is to keep it growing late in the fall by cultivation and fertilizers so that it does not harden off properly. Many plantings, representing heavy investments, fail because of lack of organic matter in the soil. This is related to water-holding and water-supplying capacity of the soil, and lack of proper fertilizer. Dr. Harley L. Crane and his assistants, in their work with tung and pecan trees, have shown the vital need for certain elements on some soils. Trees weakened by the lack of these elements are early prey for some diseases. The element most frequently deficient is nitrogen, but sometimes boron, copper, or iron is lacking; or the elements are not in balance, because of the excess of some, or the lack of others.

By adjusting the various soil, water, and site factors necessary for a continuous, vigorous growth of trees, many so-called disease conditions are eliminated. Many fungi and viruses, however, will attack trees in the pink of condition; a few of the more important of these are treated in the following sections.

+Chestnut Blight+

The destruction by blight of the native stands of the American chestnut, and of the small eastern orchard industry based on European and American chestnuts and their hybrids is almost complete. Blight has been found in the planted European chestnut orchards of the Pacific Coast from time to time, but it has been kept under control by eradication. Chestnut trees or nuts from the eastern States, where blight is common, should not be shipped into the Rocky Mountain or Pacific Coast States.

Finding the Asiatic chestnuts resistant to the blight, the Division of Forest Pathology sent R. Kent Beattie to Asia to make selections of chestnuts for introduction into this country. Later Peter Liu, a Chinese collector who worked with Mr. Beattie, continued to select Chinese chestnuts for introduction. These introductions, together with the earlier ones made by the Division of Plant Exploration and Introduction, were grown at Chico, Calif., Savannah, Ga., and Bell, or Glenn Dale, Md. Altogether some 300,000 chestnut trees, of pure species and hybrids, were distributed to cooperators for forest and orchard plantings. (Fig. 1.) These constituted a fine lot of material from many parts of Asia as a basis for selecting the best ones for our use. Private nurseries and State game and forestry departments are now growing these chestnuts and the Division of Forest Pathology has discontinued general distribution of trees to cooperators.

Chinese chestnuts have proved to be the most valuable for forest, orchard and ornamental use. The Japanese chestnut is being discriminated against because of the poor quality of its nuts. Orchardists having mixed plantings containing Japanese chestnuts are advised to top work the trees or remove them, if the seed is to be used for plantings. In fact, for orchard plantings, nuts should be used only from the best individual trees of the Chinese chestnut.

The Chinese chestnut should be planted on sites with good air drainage as it is very susceptible to injury from early-fall or late-spring freezes. Many persons think their trees have been killed by the blight when the primary cause of the trouble was injury to the trunk by freezing followed by growth of the blight organism over the injured parts. This fungus may grow for many years in the outer layers of the bark without doing any material damage to the tree. An important factor in resistance of the Chinese chestnuts to the blight is to keep the trees growing vigorously. Avoid late growth in the fall as this favors fall freezing damage.

[Illustration: Figure 1.--F1 hybrids between the Chinese chestnut and the American chestnut.]

+Nut Spoilage+

In the Southern States one of the most serious problems with some selections of the Chinese chestnut is the spoilage of the nuts. Marvin E. Fowler made a study of this trouble at Savannah, Ga., and found that most of the trouble in that restricted area was caused by a Gleoesporium-like fungus that infects the nuts at the tip.[10] Because spraying experiments did not give control, the more susceptible trees have been removed. In most parts of the South, however, this fungus is not the primary cause of nut spoilage and the limited work so far carried out has not revealed the cause. Part of the trouble may be due to physiological break-down. As individual trees vary greatly in susceptibility to this deterioration of the nuts, orchardists are advised to top work or eliminate the more susceptible trees. Some people have believed that exposure of the nuts to the hot sun while in the bur or on the ground may cause damage. The market for Chinese chestnuts can be ruined by shipping nuts that are partly spoiled by the time they reach the consumer.

[Footnote 10: Gravatt, G. F., and Marvin E. Fowler. Diseases of chestnut trees and nuts. Northern Nut Growers Assoc. Rept. (1940) 31: 110-113. 1941.]

+Phytophthora Root Disease of Chestnut+

Phytophthora root disease, caused by _Phytophthora cinnamomi_, is treated briefly here, and interested nut growers can consult the detailed earlier article.[11] Briefly, this fungus is considered as introduced into this country over a hundred years ago. It killed the chestnut and chinkapin growth over large areas in the southern States. Asiatic chestnuts are highly resistant to this disease, and when grown on well-drained soils have not been damaged. Our test plantings of Chinese chestnuts growing in the same soils where susceptible trees of American and European chestnuts were killed, continue to make a vigorous growth. The European and American chestnuts and their hybrids growing in the western States are in danger from this fungus as it has now been reported in the West. This same fungus sometimes kills thousands of young nursery trees of the black walnut, but these epidemics are usually brought on by unusual weather conditions. Poor soil aeration, induced by excessive rainfall and poor drainage, makes ideal conditions for damage to the walnut and other hosts by _Phytophthora_. Even the very resistant Chinese chestnut roots are invaded by the fungus when the soil remains waterlogged for extended periods.

+Brooming Disease of Walnut+

A systemic brooming disease, observed on planted walnuts as early as 1917, has been the subject of considerable discussion during recent years, because it has now spread widely into the native black walnut growth. In 1932 Waite published that he had been observing the disease for some 15 years but that "it was unknown on the black walnut in the wild in this country or on planted trees away from the Japanese walnut." The disease has continued to increase in prevalence in recent years and is now widely distributed in native black walnut growth in Tennessee, Virginia, District of Columbia, Maryland, Delaware, and New Jersey. This extensive spread into the native growth during the last 15 or 20 years and the fact that reports indicate that all of the early cases of the disease were found near nursery-grown trees offer some evidence that the disease is an importation from another area or continent into the eastern black walnut zone. From the literature and oral reports, it seems that the disease is now present also in North Carolina, West Virginia, Pennsylvania, New York, Ohio, and Michigan. Surveys probably would uncover the disease among native wild and planted walnuts in other States.

[Footnote 11: Crandall, B. S., G. F. Gravatt, and M. M. Ryan. Root diseases of Castanea species and some coniferous and broadleaf nursery stocks, caused by Phytophthora cinnamomi. Phytopathology 35: 162-180. Illus. 1945.]

+Economic Importance and Hosts+

The black walnut is a valuable native forest tree, widely but not abundantly distributed in the eastern United States. It is extensively planted as a forest tree. The numerous plantings and natural stands around farm homes, along fences, and in pastures are also very valuable. More and more grafted ornamentals, and orchards of black walnut are being planted. For these the per-tree investment is high.

[Illustration: Figure 2.--The brooming disease of walnut. Severe brooming on Japanese walnut.]

The ultimate effect of the brooming disease on the black walnut is not known. Dr. Waite stated, "Trees even moderately attacked soon become worthless for nut production." Some affected black walnut trees, however, continue to produce small crops of nuts. Visible symptoms have been known to disappear. In addition, some seedlings, and probably large trees also, are infected without showing symptoms. Such observations indicate the complex nature of the disease. Detailed studies are needed, but at present this Division is not in position to do more than limited, part-time work on the disease.

The butternut, a widely distributed forest tree of minor importance, is seriously injured or killed by this disease. The disease severely damages or kills the Japanese walnut, which has been planted to a limited extent but is of little importance. According to Dr. Waite's report, the Persian, or English, walnut is attacked, but very few trees of this species are planted in the eastern States. Precautions should be taken to prevent the introduction of this disease into areas where it is not now present, particularly the western states.

Symptoms expressed by infected trees are viruslike, and Hutchins and Wester[12] were able to produce the brooming symptoms on a small number of trees by means of bark patch grafts, indicating that the brooming disease probably is caused by a virus.

[Illustration: Figure 3.--Brooming disease on black walnut. Ascending type, upright, sucker growth is typical of this species.]

+Description of Symptoms+

The entire range of symptoms of the brooming disease has not been determined. Symptoms are recognizable during mid-July but they are most pronounced during September and October. Curling and cupping of leaflets, chlorosis, narrowing and basal tapering of leaflets appear to be associated with early stages of the disease. On severely affected trees there are distinct broomlike growths at branch terminals, along primary or secondary branches, or on the main stem to the ground line (Fig. 2). The broomlike growths are formed by the continuing abnormal development of normally located buds into short, succulent branches. Upright, suckerlike branches appear on primary and secondary branches and on the main stem of the affected tree. (Fig. 3).

The broomed parts usually die back during the dormant period following their appearance. The dead brooms on trees that appear to be healthy during the early months of the growing-season indicate that the trees are infected. Usually the diseased trees, even those severely affected, exhibit normal growth during the early summer months.