
185 S.E.2d 423 (1971)
13 N.C. App. 323
STATE of North Carolina
v.
Robert Lee JOHNSON.
No. 7110SC722.
Court of Appeals of North Carolina.
December 29, 1971.
Certiorari Allowed March 7, 1972.
*424 Atty. Gen. Robert Morgan, by Special Counsel Ralph Moody, Raleigh, for the State.
Russell W. DeMent, Jr., Raleigh, for defendant.
Certiorari Allowed by Supreme Court March 7, 1972.
BROCK, Judge.
Defendant assigns as error that the State was allowed to offer evidence of the transaction between defendant and the confidential informer two weeks before the search in question. He argues that this violates *425 the rule against allowing evidence of one crime to prove the commission of another. He cites State v. McClain, 240 N.C. 171, 81 S.E.2d 364, in support of his argument.
The evidence complained of by defendant was properly admitted under the exceptions to the general rule as pointed out in State v. McClain, supra. Defendant and his wife absolutely denied knowledge of the marijuana or that they had anything to do with it. Defendant also testified that he was not suggesting that a person who lived with him had anything to do with marijuana. Defendant and his wife testified that they never locked the doors to their house and were clearly seeking to leave the impression that some unknown person came to their house and secreted the marijuana while they were away. It was competent for the State to show by the challenged evidence the defendant's intent and guilty knowledge as well as his motives. See State v. Colson, 222 N.C. 28, 21 S.E.2d 808; State v. Hardy, 209 N.C. 83, 182 S.E. 831. This assignment of error is overruled.
Defendant assigns as error that Detective Watson was allowed to state that in his opinion the substance purchased by the confidential informant was marijuana. The trial judge sustained defendant's objection until the State established appropriate qualifications of the witness to give his opinion. This assignment of error is without merit. Detective Watson testified that he had studied the identification of various drugs, including marijuana; that he was familiar with the plant in its growing form; that in his work he had been observing marijuana for the last five or six years; that he was familiar with its appearance and its odor; and that during the last two or three years he had been engaged in work with marijuana on a weekly basis. Based upon this familiarity with, experience with, and knowledge of marijuana, the trial judge allowed Detective Watson to express his opinion that the substance purchased by the confidential informant was marijuana. The trial judge did not commit error in this respect.
"The competency of a witness to testify as an expert in the particular matter at issue is addressed primarily to the discretion of the trial court, and its determination is ordinarily conclusive unless there is no evidence to support the finding or unless there is an abuse of discretion." 3 Strong, N.C.Index 2d, Evidence, § 48, p. 677.
The trial judge in this case did not make an express finding that Detective Watson was an expert, but defendant did not state that his objection to the testimony was on the grounds that the witness was not an expert. In the absence of a request for a finding by the trial judge as to the qualification of the witness as an expert, it is not essential that the record show a specific finding. In the absence of such request, the finding by the trial judge is implicit in his ruling upon the admissibility of the evidence. State v. Perry, 275 N.C. 565, 169 S.E.2d 839.
Defendant next assigns as error that the trial judge refused to allow defense counsel to question the police officer concerning the identity of the confidential informant.
"... A defendant is not necessarily entitled to elicit the name of an informer from the State's witnesses. (citation) The Government's privilege against disclosure of an informant's identity is based on the public policy of `the furtherance and protection of the public interest in effective law enforcement'. (citation) However, the privilege must give way `where the disclosure of the informer's identity, or of the contents of his communication, is relevant and helpful to the defense of the accused, or is essential to fair determination of a cause....' (citation)" State v. Moore, 275 N.C. 141, 166 S.E.2d 53.
Defendant relies upon Roviaro v. U. S., 353 U.S. 53, 77 S.Ct. 623, 1 L.Ed.2d 639 *426 (1957). In Roviaro the confidential informer had taken a material part in bringing about the possession of certain drugs by the accused, had been present with the accused at the occurrence of the alleged crime, and might be a material witness as to whether accused knowingly transported the drugs as charged. In the instant case the activities of the confidential informer were only collaterally connected with the offense for which defendant was on trial. There is no showing that the identity of the confidential informer would be relevant or helpful to defendant's defense against the charge upon which he was being tried. The only evidence concerning the informer was the testimony of Detective Watson relating what he (the officer) observed.
No error.
BRITT and VAUGHN, J J., concur.
