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has been brought about because of increased soil organism activity following continued use of 2,4-D? DR. CHILTON: NO, it's no worse than it was several years ago. We have never recommended 2,4-D by itself where we have Johnson grass. With respect to the Lactuca, it's treated with apostemergepce spray, so the microbial decomposition will not enter into its lack of control. (Hawaii) : Was the chemical applied to the interrow and not on the cane ? L. THEVENIN DR. CPILTON:NO, it was applied on the llne. The chemical is always put where the cane is, not the middle where the tractor wheels go. We always cover the 2 f t , in the row and cultivate the side. z R. WOLD(Hawaii) : How often is cultivation practiced during a crop ? ' DR. CHILTON: It depends on whether it rains or not. The drier it is, the more they cultivate. I don't think it's necessary but they feel that theyshould get out in the field and cultivate as much as they can. If i t rains, they can't cultivate. They try t o make 5 cultivations as a rule. It's not just weed control, because what they're trying to do is build up the row to cover in the cane gradually after the cane suclrers.

CHEMICAL WEED CONTROL IN HAWAII* NOELS. HANSON Exfieriment Station, HSPA, Honolulu, Hawaii Chemical control of weeds in the Hawaiian sugar industry began in 1913 when experiments with sodium arsenite were installed at Olaa Sugar Company on the Island of Hawaii, following a suggestion by H. P. AGEE,Director of the Experiment Station, HSPA, to C. F. ECKART, Manager of Olaal. From 1913 until 1944, sodium arsenite in water was the main herbicide used for weed control in sugar cane fields in Hawaii. During the 1930's and early 1g40Js,sodium chlorate found some use, but its application was limited due to fire hazard. Diesel oil was used on some plantations2?3. In 1944, a series of experiments was started by F. E. HANCEand F. C. DENISONwith oil-water emulsions activated with sodium pentachloropheqate. This led to development of a stable concentrated activated diesel emulsion known as CADE4. The use, as contact sprays, of this and a later formula developed in 1953 which incorporates aromatic oil and is known as ARCADE, and straight aromatic oil have replaced arsenicals as herbicides in this industry. In I945,2,4-D came into use as a translocated herbicide, and as a pre-emergence treatment in 1947. Since the latter date, this chemical has had an integral part in the weed control program on all Hawaiian sugar plantations. Both the arsenicals and z,4-D were effective in controlling broad-leaved, dicotyledonous plants, but were relatively ineffective on maliy grasses and sedges. Consequently by 1948, weed populationsin ,many.plantatian fields wes.e,daminated by,several pernicious,grasses6. In t,hat year, a grass killer, sodium TCA, became available. Plantations are in operation today that probably would not have survived if grasses such as n no do^ dactylon Bermuda 1 grass, Panicum repens torpedo grass, Panicum fiurfiurascens tall panicum, and Pasfilurn conjugaturn Hilo grass, had not been brought under c o ~ t r o l i " In 1951, CMU (monuron) and in 1953, DCMU (diuron) became available. These herbicides lengthen the period of pre-emergence control beyond that of z,4-D, and are even mo?&effective on a broader spectrum of species when sfjplemented with \

* Published

""1

with the approval of the Director as Paper No. 66 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association, Honolulu, Hawair.

,

NOEL S. HANSON

539

z,4-D. A more effective grass killer than sodium TCA, sodium dalapon came into general use in 1953. I t is in extensive use at present, but must be applied carefully to avoid injury to sugar cane. Other herbicides, such as simazine, silvex and amitrol, have been tested extensively and may be used when registration with the United States Department of Agriculture has been completed. Major Weed Problems In addition to a broad spectrum of non-rhizomatous species of broad-leaved and grassy weeds, there are several rhizomatous species, mainly grasses including those listed above, that constitute special problems in and adjacent to sugar cane fields. Some of the major species found in-field are listed. Non-rhizomatous s*ecies Grasses (Monocots) Digitaria pruriens - slender crabgrass Digztaria sanguinalis - hairy crabgrass Digitaria violascens - Violet crabgrass Digitaria pseudo-ischaemum - creeping crabgrass Eleusine indica - wiregrass Chloris radzata - plushgrass Chloris inflata - swollen fingergrass Echznochloa colonum -jungle rice Broad-leaved (Dicots) Amaranthus spinosus - spiny amaranth Portulacca oleracea - purslane Crotalaria incana - hairy rattlepod Crotalaria saltzana - smooth rattlepod Euphorbia hypericifolia - graceful spurge Emilia sonchifolia - Flora's paintbrush Leucaena glauca - false koa Ricinus communis - castor bean Erechtites hieracifolza - fireweed Rhizomatous, stoloniferous, bulbous or tuberous species Grasses Cynodon dactylon - Bermuda grass (manienie) Panicum purpurascens - tall panicum (paragrass) Panzcum repens - torpedo grass Paspalum conjugatum - Hilo grass Impomoea spp. - morning glories Tritonia crocosmaeflora - Portugese lily Commelina digusa (hono-hono) Sedges Cyperus rotundus - nut grass Cyperus esculentus - giant yellow nut grass Cyperus brevifolius - green kyllinga Cyperus polystachyos - field sedge

Herbicide-tolerant strains of some species have been found. Two sodium dalaponresistant strains of Cynodon dactylon have been isolated. One strain from Kilauea Sugar Company on Kauai and another strain with somewhat different morphological References p. 547.

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characteristics from Honokaa Sugar Company on the Island of Hawaii, have shown high tolerance to dalapon as compared with a strain from the Experiment Station in Honolulu (Fig. I). A strain of Commelina di#usa, resistant to z,4-D but not to 2, 4, 5-T, was found at Paauhau Sugar Company on the Island of Hawaii. These resistant strains of both species are presently under study at the Makiki Experiment Station.

Fig. I. Effects of 5, 10 and 20 lbs. per acre treatments of sodium dalapon on 3 strains of Bermuda grass Cynodon dactylon. The Kilauea and Honolraa strains were later treated for a total of 6 treatments a t the same levels and still remained alive. The Makiki strain was destroyed with the second treatment of each level.

There appears to have been a definite increase in tolerance to 2, 4-D by Erechtites hieracifolia plants in present populations as compared with those in populations sprayed with z,4-D from 1945 to 1950. I t is to be expected that as spraying of particular herbicide continues, genetic segregation may in time yield strains of plants with increased tolerance to that herbicide.

1

~

Scofie of Chemical Weed Control At present, nearly all weeds in the sugar-cane fields in Hawaii are controlled with herbicidal sprays. More than 500,000 acres are sprayed each year at a cost of over $6,ooo,ooo. This amount represents the cost of such chemicals as CMU, DCMU, 2 , 4-D, sodium dalapon, sodium TCA, PCP, aromatic and diesel oils, emulsifiers and wetting agents, as well as labor and other costs of application. During the last 10 years, application methods have been improved to such an extent that low gallonage sprays .of from 2.5 to 50 gallons per acre are adequate for satisfactory weed control. Spray planes (Fig. z), spray tractors (Fig. 3), and spray men with pressurized stainless steel knapsacks (Fig. 4) apply the herbicides. Spray units are supplied from centralized mixing plants by tank trucks. For refilling the knapsacks of spray men, herbicides are pumped through hoselines under pressure to areas being treated. Program of Testing Herbicides All new herbicides for testing are first submitted to the Chemistry Department of the Experiment Station, HSPA, for initial screening and formulating for use in sugar cane. The more promising materials then go to the Agronomy Department and

NOEL S. HANSON

t o the Island Representatives for field testing on the plantations. Eventually they go into plantation use if their effectiveness for weed control compares well with herbicides already in use. Observation and yield tests are conducted in plantation fields to evaluate the effect of the herbicides.

Flg.

Spray plane applying herbicide. Rebuilt Stearman biplanes are operated commercially. CMU a t 3 to 5 lbs. per acre is applied in water as the main pre-emergence treatment.

2.

Fig. 3 . Spray tractor applying z,4-D and sodium dalapon. The nozzles are carried on skids in order that the spray height can be kept independent of pitch or roll of the tractor operating on uneven ground.

Evaluation procedure is as follows8. Observation tests are installed in small plots in randomized blocks. The chemical are applied as timed, calibrated sprays by pressure knapsacks with multi-nozzle boomss. These tests are graded regulary. Tests for yield are also conducted. Weekly gradings of effect are based on abundance of weeds ands on degree of control according to the following indices : References

p. 547.

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Weed control zndex I 2

3 4

5

Condition observed No apparent effect Slight control Moderate control Satisfactory control Complete kill

Grading may be done to half points, i.e., 4.5 or 3.5. Index 4.0 is the point at which a plot or field is about to go out of control and where respraying should be scheduled. The number of days control is assigned according to the graph in #ig. 5 which is based on the average of four replications. This graph is a running record of control. Conse-

-

-

--

--

543

NOEL S. HANSON

amend deleterious conditions in the soil microflora or fauna complex. Improvement over the untreated plants may also be due to reduced competition through effective weed control. Growth measurements and leaf color are recorded in some tests. Measurements are made mainly of stalk elongation, and leaf color indices are recorded in relation to the cane effect indices. Yield data on cane and sugar are obtained in the usual manner. Plots 40 ft. by 40 ft. are used as a standard. For observation tests, I/IOO a-cre plots, 4 lines wide are used and are placed in randomized blodks with 4 replications. With the s'ystem of evaluation outlined above, a large number of tests are conducted each year in plantation fields under many conditions of soil and moisture at various elevations. These are used as the bases for larger scale block tests to study costs and practicability of using promising new chemicals in the plantation weed control programs.

Number of days after treatment Fig. 5. Weed control log.

Expt. No. 49.39 Location K a h u k u Plantation Co. Fd. No. 2 Sugar Cane Variety 37-1933 Ratoon Irrig. Soil Type Gray hydromorphic soil. Equipment used Experiment spray u n i t Comments : Average of four replications. Predominant weeds were ricegrass, graceful spurge, Flora's paintbrush and sow thistle.

Legend CMU in ARCADE DCMU in ARCADE - - - - - = Check Bar Graphs = Inches rainfall -

--

=

-

Weed control index

Condition observed

I 2

No apparent effect Slight control Moderate control Satisfactory control Complete kill '

3 4 5

Pre-emergence Herbicides Studies in the late 1940's showed that 2, 4-D and related compouAds were effective in pre-emergence control for about 3 weeks. Since 1951, CMU, DCMU, and more recently simazine, have shown periods of pre-emergence control up to 2 months or .longer. These 3 herbicides are of particular value during the germination period in sugar-cane since there have been no deleterious effects on germination (Fig. 6). 2,4-D and sodium dalapon have had a considerable effect on germination when applied t o uncovered seed pieces, as shown in Fig. 7. 2, 4-5-T and sodium TCA have caused similar effects. Reduced stands have occurred where 2, 4-D and 2, 4, 5-T have been applied to relatively porous soil prior .to germination. Damage to sugar-cane from CMU and DCMU has occurred on soils low in organic matter, as in Fig. 8, on sandy References p. 547.

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Fig. 6. Germination of sugar cane Variety 37-1933 after treatment of the seed pieces with CMU and simazine a t 5 lbs. in 50 gals. water. Seedlings from the treated seed pieces are about equal to the untreated checlr plants.

'

spots, or where shallow soils are underlaid by rocky or gravelly subsoils. Where sugarcane has been under stress in such areas due to deficiency in moisture or nutrients, damage from both CMU and DCMU ha$ been observed. Damage from DCMU has always been less than from CMU. Tests in such areas have shown less damage from simazine than from either CMU or DCMU. Likewise less damage has occurred from spraying simazine over the sugar-cane plants than with either of the other herbicides, including 2, 4-D and related substances. Tables I and I1 give the comparative effectiveness of 4 herbicides for pre-emergence weed control.

Grass Control with Translocated Herbicides In the control of rhizomatous grasses such as Bermuda grass Cynodon dactylon,

Contact Herbicides Contact control of non-rhizomatous grasses and broad-leaved plants is achieved a t present with the activated emulsions: CADE and ARCADE. some spraying of straight aromatic oil is done in the high rainfall areas. Experiments are in progress

it

NOEL S. HANSON

Fig. 7. Effects of z,q-D, amine salt and sodium dalapon on germination of seedpieces of Variety 37-1933 after treatment with 5 lbs. of the active herbicide per 50 gals. water. The z,4-D treated seedpieces did not germinate. Only stunted shoots emerged from the sodium dalapon treated seedpieces.

TABLE I OF RELATIVE EFFECTIVENESS O F CMU, DCMU, SIMAZINE AND 2,4-D F O R PRE-EMERGENCE OF NON-RHIZOMATOUS WEEDS,WITH Digitaria sanguinalis HAIRY CRABGRASS AS THE DOMINANT SPECIES ON HYDROL HUMIC LATOSOL FROM KILO SUGAR COMPANY

COMPARISON

CONTROL

Treatment CMU, (monuron) DCMU, (diuron) simazine z,q-D, iso-octyl ester Control (no treatment)

*

Diluent water

,,

Active 1bslA

Rainfall during test period

4.0 4.0 4.O 4.0

44.25 in. ,, , ,

-

,,

,, ,,

I,

,,

I,

A v . days control Total Net '59 76 76 43 33 *

36 43 43

Eflect on cane I .o

1.0

10

1.0 1.0

o

I .o

Some rhizomatous species not controlled by pre-emergence emerged earlier.

TABLE I1 OF CMU, D C M U AND S I M A Z I N E FOR PRE-EMERGENCE CONTROL O F NON-RHIZOMATOUS WITH Digitaria sanguinalis HAIRY CRABGRASS DOMINANT ON HUMIC LATOSOL FROM

COMPARISON

WEEDS

PAAUHAU SUGAR COMPANY

Treatment CMU, (monuron) DCMU, (diuron) simazine Control (no treatment)

References 9. 547.

Diluent water

,,

Active ZbslA

Rainfall during test period

4.O 4.0 4.O

13.69 in.

-

,,

,, ,, ,,

,I I)

A v . days control Total Net 32 34 38 19

Eflect o n cane

I3 15 I9

1.0

o

1.0

1.0 1.0

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NOEL S. HANSON

547

control and 2, 4-D or 2, 4, 5-T for pre-emergence control are effective and are in common use throughout the industry.

F u t w e Outlook I t has been shown that strains of sodium dalapon-tolerant Cynodon dactylon and 4-D-tolerant Cornrnelina d i f u s a have arisen as a result of continued use of these herbicides in field. For this reason it is necessary to continue the formulation and testing of new types of herbicides with different modes of action on weeds. Diversification in the use of herbicides infield will be necessary to bring the various modes of action to bear upon those plants which have high tolerance fbr some chemicals. 2,

REFERENCES ECKART, C. F., 1913. Report of the Committee on Cultivation and Fertilization on Unirrigated plantations. Hawazzan Planter's Record, 10 ' 101-105. 2 HANCE, F. E., 1931. Weed Control. Proceedings of the Fifty-first Annual Meeting of the Hawa~ianSugar Planter's Association, 51 . 257-309. 3 HANCE, F. E., 1938 Chemical Weed Control. Hawazzan Planter's Record, 41.No. I : 3-37. 4 HANCE,F. E., 1948. Weed Control on Hawaiian Sugar-Cane Lands - Contact Herblcides. Hawazian Planter's Record, 52.No. 2 : 93-105. 6 HANSON, NOELS., 1948. Weed Control Experiments and Practices in Sugar-Cane Production. Hawazian Pla?zter's Recovd, 52.No. 2 : 113-154. 6 HANSON, NOELS., 1948. The Mechan~csof Spraylng Herblcides for Weed Control. Reeorts of the Hawaiian Sugar Technologzsts. 11 ' 83-102. 7 HANSON, NOEL S , 1955. Forms of Substituted Urea as Herbicides for Controlling Weeds on Sugar-Cane Lands of Hawaii. Doctor's Thesis : 1-86. 6 HANSON, NOEL S. and BUMANGLAG, JOSE, 1957. Testing of New Herbicides. Report of the Haze~aiianSugar Technologists. I 7 : 130-133. 1

DISCUSSIONS W. H. C. KNOWLES (Jamaica). What would be the practical means of eliminating resistant strains of weeds before they become widely established ? N. S. HANSON (Hawaii) : I thinlr that the way it 1s going to be accomplished is through the use of combinations of herblcides. You have seen suiile Bermuda grass which is tolerant to dalapon and to TCA. I don't thlnk ~thas been a matter of tolerance developing since we started using these materials. I think that thrcugh segregation that has gone on in years past, these tolerant strains Bermuda grass we have a species that reproduces largely asexually from root have evolved. W ~ t h stocks. On the other hand, we may have a species such as fireweed which reproduces entirely from seed. We would expect that tolerant strains would evolve much more rapidly where each population of weeds grows from true seed rather than from root stoclrs as in Bermuda grass. L. A. THEVENIN (Hawaii). Would you comment on the effect of dalapon under drought conditions ? DR. HANSON. Where you have conditions for optimum growth, translocation in the plant goes on a t the optimum rate. Under extremely dry conditions, translocation 1s reduced. When applied under wet conditions there is a possibility of the cl~emicalbeing washed off the plant and that is one of the reasons why Dr. Hilton is looking Into the posslble use of an mvert-type emulsion, the water-in-oil type which can be applied under rainy conditions. M. ISOBE(Hawall): I n evaluating soil tolerance to CMU and DCMU, do you think the addition of complete fertilizer to eliminate the nutrient factor gives a better ~ndicatloilof soil tolerance to these herblcides ? DR. HANSON. The application of fertilizer in a plantation program may not be adequate, particularly in spots, to provide optinlum growth. If the cane plant 1s under distress from any factors, herbicides may be damaging. F. J . FLOYD(Jamaica) : What are the methods of weed control in earth canals, both when dry and when carrying water. There has been some work done on that here. I n areas that can be dried out, DR. HANSON: we have run a number of tests with CMU and DCMU. We are now recommending 10 Ibs. per acre as a first application to be followed wlth 5 lbs. per acre as needed throughout the crop for ditches and canals. For areas where water stands In the ditch, either drainage ditch or canal wit11 standing water, we would recommend fish. At Kelraha Sugar Company on Icauai the use of the fish Tzla$za

.

548

AGRICULTURE

mossambica has been as practical a means of control as we can possibly get. There has been some use of chemicals, but the TilaPia have been highly effective. R. F. INNES (Jamaica): Is there any legislation In Hawaii on weed control chemicals ? Any Federal Laws ? DR. HANSON: Yes, there is a law here which deals with the use of z,4-D and related-compounds that was first passed in 1949 and amended in 1951. Since that time there have been attempts to pass additional legislation. The law is under jurisdiction of the Territorial Board of Agriculture and Forestry. The Director of the Division of Entomology and Marketing handles phases of this law. He issues permits to users and registers the distributors. There is a charge of 2 cents per lb. on z,4-D to cover the handling of that legislation. As far as the sugar industry is concerned, there is somewhere between 15% and 20% of our area where 2,4-D cannoit be used and we are continuing to have difficulties from spray drift even in spite of that. Recently we had 4 cases where contaminated equipment going into the restricted areas has caused some difficulty. I have come to the conclusion that the way to get rid of ~ , 4 - ~ t r o u b lis e sto get rid of z,4-D. The Federal Law was an amendment to the Pesticide Act and operates in this way, that before a new compound, such as CMU, DCMU or dalapon, can be used on a crop, i t has to have a label registration and evidence has to be shown to the Food and Drug people that there is not any toxic residue of the chemical in the particular plant. Each crop has to be covered separately. There are 4 categories of those chemicals. One is for those chemicals that are so low in their toxicology that there is no need of a tolerance. On the other hand, there are those which are so highly toxlc that no tolerance can be permitted. Then there is a group such as CMU, DCMU and dalapon, where tolerance has actually been set through feeding trials and tissue analyses. A11 the others, which include such things as z,4-D and pentachlorophenol, which were sold and came into the picture before the pesticide amendment, have to be handled on a no-residue basis. L. J. WOODS(Australia) : What has been your experience in the use of hellcopters for applying herbicides as to (a) efficiency of application and (b) cost of application, as compared with application by fixed-wing aircraft ? DR. HANSON: I t can be done cheaper with the fixed-wing type. One advantage of a helicopter is t h a t it can be set down on the edge of the field, pick up a load and spray that field. However, right along with that comes the disadvantage that to move from one field to another you have t o move all the supply equipment. The fixed-wing plane operates from an airstrip and actually, i n addition to doing the spraying, it transports the material. In operatmg from a central strip, that plane sprays the field and if i t has a partial load left, it can go on to spray another field and there isn't time lost in taking equipment over. H. EVANS(Jamaica) : When we were testing dalapon in the first instance, we did not get a very good response to I application. Later on we got very excellent control with repeated small applications, so much so, m fact, that we could get as good results w ~ t h3 applications of 2 Ibs. per acre a t 10 or 1 2 day intervals as we could get with 25 lbs. per acre a t I application. I would like to ltnow ~f you have had s~milarexperience. : Definitely, repeated applications are to be preferred over the single application. DR.HANSON Most of the dalapon applications here are a t 1/10 of a lb. per acre, then repeated once or twice; 29 lbs. per acre until finally you are rid of the over a uniform mat, I would say that 24 $- 26 grass. What happens is that you get a certain percentage on first application, some more the next time, until you get on down to spot spraying. DR. EVANS:In the distribution of herbicides by plane, what modifications have you made in your equipment in the last couple of years ? DR. HANSON : When the airspray equipment was first set up here i t was necessary to put in a n extensive valve system on the boom in order to shut off each nozzle independent of the other. Since the development by the Spraying System Company of the diaphragm type check valve, t h a t type has been used. More recently, trailing edged booms have been put into use and there are varlous other modifications. The difficulties in pattern is the matter of the arrangements of nozzles on the boom. I would like to ask if any of you are having difficulties with witchweed, Striga species. I know there are areas in the sugar-cane world where Striga is a problem. It has within the last 3 years become somewhat of a problem in the Carolinas, on corn particularly. I t will grow on the weed Dzgitaria. It also grows on the roots and sends haustoria into the t~ssuesof the host plant and can be very damaging. R. FARQUHAR (Australia) : We have had a little trouble with Strzga. When we cleared some new land for cultivation from vlrgln forest we got sporadic attacks of Strzga a t that tlme. We were a bit concerned about it. We sprayed it with z,4-D and got a complete lcill. DR. HANSON: HOWabout the species Passzfiora puclzella ? Do any of you have difficulty with t h a t ; have you been able to control it ? I t is a problem on I plantation here and so far trichlorobenzoic acid bas been the most effective control. I-I. GOMEZ(Hawail): Did the 2,4-D treated seedpieces eventually germinate after 21 days shown in the time lapse pictures ?

+

a

E. ROCHECOUSTE

549

N. S. HANSON (Hawaii): No. I would judge that the coverage of these seed pieces by dipping was somewhere between 100 and 150 gals. per acre, which would be 10 to 15 Ibs, of z,q-D. ~t Tv~uldn't be as serious where you're applying lesser amounts in the field. However, you could some damage. We have seen up to 50% reduction in germination from 5 lbs. applied in 25 gals. sprayed over the seed. L. THEVENIN(Hawaii) : I s there any solution to the problem of poor CMU control in factory areas due to carbon deposits ? DR. HANSON:There appears to be adsorption of the CMU on organic matter or on active carbon. There is an area of this type a t HC&S. I n fields to the leeward of the Paia mill, where soot has been deposited, there is a question whether you can economically get good control with CMU. 1think i t is largely a matter of resorting to contact herbicides in those fields a t HC & S. MR. THEVENIN: DOYOU have any information on the effect of traffic to cane fields, following pre-emergence herbicide operations in relation to the degree of control experienced ? DR. HANSON: It was more of a problem when we were using z,q-D pre-emergence in that equipment moving through the fields and disturbing the soil would disturb the chemical blanket to the extent that weeds could come up in those areas. With CMU it hasn't been as serious a problem. N. H. MONTEITH (Fiji) : What are your results with simazine and atrazine ? What is the cost of time-lapse equipment ? DR. HANSON: AS far as simazine is concerned we reported on 23 tests a year ago. Most of them showed longer control for simazine than for CMU. The results were more nearly equal with DCMU. It depends to some extent upon moisture, what the location is, and also on weeds present. Simazine in our tests has done very well. With species 1ilce.fireweed that we mentioned previously, it has appeared that simazine has given us somewhat better control and actually has done less damage t o cane. There are also some cases of shortage of moisture or where the timing isn't r ~ g h with t simazine, one will not get the control that results from either of the substituted ureas. We have hoped that there would be registration of a.label for simazine soon. However, I learned about a week ago that the data which have been submitted from various parts cf the world have not proved whether or not simazine has a zero residue in sugar cane; consequently, label registration has been denied. Relative to cost of time-lapse equipment as you saw it would be for I camera unit with timers, automatic switches, etc., would be between $800 and $~ooo. MR. THEVENIN: What is the status of biological weed control in the sugar-producing areas of the world ? DR. HANSON: There has been a great deal of worlc on biological control done here by the Board of Agriculture and Forestry. I thinlr many of you are familiar with the excellent worlc that was done in Australia on the Cactoblastis cdctorum. The Cactoblastis larvae mere brought to Hawaii by Dr. Fullaway and have been established here and are doing a good job of controllmg the prickly pear cactus, Opuntia megacantha. You may have seen a story in the paper here within the last week that the species of Syngamza 1s doing a very good job on lantana control. The pamakani Eu@atorzum adcnophoruwz is another example. At Ulupalakua Ranch there was a time when the Maui pamakani had talren over large areas of ranch land. Through the introduction of the parasite, that particular species has been drastically reduced.