Apple seedlings cv. Golden with 5 - 6 leaves were preventively or curatively sprayed with dithianon. Different concentrations: 0.25, 0.50, 1 (field dose) and 2 g/L as commercial formulate of Delan (70 WG, 70% a.m., BASF) were used in preventive treatments. In curative ones only the field dose (1 g/L) was used

In preventive ones, 24 hours after applications, the plants were inoculated with a suspension of conidia by populations of V. inaequalis with a concentration of 1 - 2 × 10⁵ conidia. After 48 hours of incubation with continuous wetness and 20˚C as mean temperature, the leaves of seedlings dried up and the curative application was realized. Subsequently all plants were incubated for 20 - 21 days at about the same temperature. In the end, the assessment of infection was carried out as mean percentage of scabbed leaf area and relative efficacy (%)*. The control, in field and in vivo trials, is classified as “good” when efficiency % is superior to 90% and “poor” when it is inferior. Statistical elaboration on grafted apples will give a more precise value of “good or poor control” in thesetrials.

Relativeefficacy   % = degreeofinfectionoftest − degreeofinfectionoftreatedsample × 1 00 degreeof   infectionoftest

After the two previous assays, a new type of in vivo trials (for dithianon) was by me pointed out and realized on potted grafted apples cv. Imperatore Dallago (very sensitive to scab, comparable to cv Mc Intosh), two or three years old, with 4 - 6 branches.

The two groups of populations were compared: sensible (well controlled ones) confronted with the poorly controlled ones with suspects on dithanon, while wild-types were not utilized, considering the high amount of work and being less essential for the comparison respect the last two types. The sensible ones were represented by a population (n.608) well controlled in Ravenna province and another sensible defined “mixed” constituted by conidia of several populations (already declared “In Vitro tests”).

In comparison, populations from Emilia-Romagna Region and Trentino Province with suspects of reduced control by dithianon were tested (poorly controlled).

From two to four replications were carried out for every population. In each test and population, four plants were inoculated: two as control ad two treated with dithianon. The application was realized 16 hours before the inoculation and every plant was treated with about 35 ml of dithianon as commercial product Delan 70 WG (70% active material), BASF using 1 g/L. The last formed leaf of every bud was detected with a plastic bind and application was realized with a handle mechanic sprayer, until the drip limit.

Inoculations were realized utilizing, for each plant, about 0.007 g of scabbed leaves and 14 ml of distilled water. The amount of scabbed leaves and water was soaked, filtered and the conidia concentrated 0.8 - 1.3⁵ /ml.

They were maintained in glasshouse with a temperature about 20˚C and relative humidity 60% - 98%, while the assessment of infection was realized 21 - 24 days after inoculation on 30 - 60 leaves/plant, evaluating the percentage of scabbed leaf area. The data were transformed in relative efficacy %*.

The relative efficacy of dithianon was calculated starting from the mean percentage of scabbed area on leaves of the group of sensible and well-controlled populations, compared with that of suspected ones. Activity data, expressed as efficacy (%), were subjected to Bliss transformation (arcsen√efficacy %) and elaborated as “incomplete and unbalanced randomized blocks” design (SAS 9.0). This program was used for the different number of tests for every sample and, The C.I. (Confidence Interval) on efficacy (%) of sensible and well controlled populations was used to identify a suspected population, as statistically different (Table 4).

Table 3 reports the results referred to the degree of infection and to the efficacy (%) of dithianon applied on several populations inoculated both preventively (with different doses) and curatively (only field dose).

The data show low or moderate levels of activity by dithianon, not only in reduced doses (until 1/4 of field dose), but also at field dose on both the types of tested populations (well or poorly controlled). Increasing the dose (from 1/4 to 2x), the degree of infection generally does not show reductions and consequently the efficacy % does not increase. The same tests replicated on population n. 99 (another well controlled population) show very uneven results, irrespective of each concentration. Likewise curative applications offer moderate or low levels of activity on well or poor controlled populations.

* Concentration that reduced germination by 50% respect test; ** Concentration Minimum Inhibiting; *** Referred to the last two or three years; **** Not Detected.

* Values statistically non-significant; ** Values statistically significant; *** Resistance Factor respect wild-types.

* Mean percentage of scabbed area on apple leaves; ** Efficacy %; *** Field dose dithianon: 1 g/L; **** “Good control or well controlled” when efficacy % is superior to 90%; “poor control” when it is inferior and with suspects on dithianon.

Table 4 presents each type population, populations, their location and results (relative efficiency %) obtained in each subpopulation. It is visible that there are moderate differences among efficacy % of all populations, both sensible and “suspected of reduced control”.

Table 5 presents statistic elaboration where C are sensible and well controlled populations, while N are those “Suspected of reduced control” and RC all the populations. General statistic diversity presents P > 0.019, so among all populations there are not statistical differences.

We chose the C as referring group, calculating mean percentage. The results expressed as relative efficacy show that the highest levels in assays are presented by good-controlled populations (n. 608 and “mixed”) with values from 100 to 93.3%, with a mean as 96.9% and a confidence interval of 10.6. So subpopulations inferior to an efficacy of 86.6% are considered statistically different.

Suspected samples (Table 4) from Emilia-Romagna region show that five populations (n.704, 603, Ba3, 2915, 601) present non significant values of dithianon efficacy (%) in all subpopulations.

The other four populations (n.501, 602, 615 and 3015) show a part of trials where subpopulations evidence significant reductions of activity by this fungicide, with values inferior to the I.C. (Confidence Interval). In Trentino Province (Table 4) only populations n. 16, 21, 23, 24 present one assay with significantly inferior values. The others, n. 17, 19 and 25 present no significant values of all subpopulations

* Reduction of efficacy (%) out of the Limits of Confidence, so statistically significant.

These reductions are generally light (efficacy percentage superior to 80%) and only two subpopulations (one from sample n. 501 and one from n. 615) present efficacy values inferior to 80%.

With referring to samples from Trentino Province, three populations (n.17, 19 and 25) respect seven total, show light reductions of activity, that are inside “confidence interval”. On the contrary four populations (n. 16, 21, 23, 24) present, in one of the two realized tests, a subpopulation with efficiency values inferior to C.I. of well controlled ones. Nevertheless, the reduction of activity percentage is moderate, with relative efficiency always superior to 80%.